Update to Go 1.21.

[sengi]

• Build container image with Go 1.21.
• Raise minimum Go version to 1.21 and update all the dependencies.
• Silence a false positive from recent versions of the gosec linter.

Tested: go test all passes (except for a couple of third-party tests in globalsign/mgo that have been broken since forever)

go test all output

ok  	bufio	(cached)
ok  	bytes	(cached)
ok  	compress/flate	(cached)
ok  	compress/gzip	(cached)
ok  	container/list	(cached)
ok  	container/ring	(cached)
ok  	context	(cached)
ok  	crypto	(cached)
ok  	crypto/aes	(cached)
ok  	crypto/cipher	(cached)
ok  	crypto/des	(cached)
ok  	crypto/dsa	(cached)
ok  	crypto/ecdh	(cached)
?   	crypto/internal/boring/bbig	[no test files]
ok  	crypto/ecdsa	(cached)
ok  	crypto/ed25519	(cached)
ok  	crypto/elliptic	(cached)
ok  	crypto/hmac	(cached)
?   	crypto/internal/boring/sig	[no test files]
ok  	crypto/internal/alias	(cached)
ok  	crypto/internal/bigmod	(cached)
ok  	crypto/internal/boring	(cached)
ok  	crypto/internal/edwards25519	(cached)
ok  	crypto/internal/edwards25519/field	(cached)
?   	crypto/internal/randutil	[no test files]
ok  	crypto/internal/nistec	(cached)
ok  	crypto/internal/nistec/fiat	(cached) [no tests to run]
ok  	crypto/md5	(cached)
ok  	crypto/rand	(cached)
ok  	crypto/rc4	(cached)
ok  	crypto/rsa	(cached)
ok  	crypto/sha1	(cached)
ok  	crypto/sha256	(cached)
ok  	crypto/sha512	(cached)
ok  	crypto/subtle	(cached)
?   	crypto/x509/internal/macos	[no test files]
?   	crypto/x509/pkix	[no test files]
?   	encoding	[no test files]
ok  	crypto/tls	(cached)
ok  	crypto/x509	(cached)
ok  	embed	(cached) [no tests to run]
ok  	encoding/asn1	(cached)
ok  	encoding/base64	(cached)
ok  	encoding/binary	(cached)
ok  	encoding/csv	(cached)
ok  	encoding/gob	(cached)
ok  	encoding/hex	(cached)
ok  	encoding/json	(cached)
ok  	encoding/pem	(cached)
ok  	encoding/xml	(cached)
ok  	errors	(cached)
ok  	expvar	(cached)
ok  	flag	(cached)
ok  	fmt	(cached)
# github.com/globalsign/mgo
vendor/github.com/globalsign/mgo/gridfs.go:681:2: github.com/globalsign/mgo.debugf format %s has arg offset of wrong type int64
vendor/github.com/globalsign/mgo/session.go:3888:4: github.com/globalsign/mgo.debugf call needs 1 arg but has 2 args
?   	github.com/alphagov/router	[no test files]
?   	github.com/alphagov/router/logger	[no test files]
?   	github.com/beorn7/perks/quantile	[no test files]
?   	github.com/cespare/xxhash/v2	[no test files]
?   	github.com/davecgh/go-spew/spew	[no test files]
?   	github.com/getsentry/sentry-go	[no test files]
?   	github.com/getsentry/sentry-go/internal/debug	[no test files]
?   	github.com/getsentry/sentry-go/internal/otel/baggage	[no test files]
?   	github.com/getsentry/sentry-go/internal/otel/baggage/internal/baggage	[no test files]
?   	github.com/getsentry/sentry-go/internal/ratelimit	[no test files]
?   	github.com/getsentry/sentry-go/internal/traceparser	[no test files]
?   	github.com/globalsign/mgo/bson	[no test files]
?   	github.com/globalsign/mgo/internal/json	[no test files]
?   	github.com/globalsign/mgo/internal/scram	[no test files]
?   	github.com/go-logr/logr	[no test files]
?   	github.com/go-logr/logr/funcr	[no test files]
?   	github.com/golang/protobuf/proto	[no test files]
?   	github.com/google/go-cmp/cmp	[no test files]
?   	github.com/google/go-cmp/cmp/internal/diff	[no test files]
?   	github.com/google/go-cmp/cmp/internal/flags	[no test files]
?   	github.com/google/go-cmp/cmp/internal/function	[no test files]
?   	github.com/google/go-cmp/cmp/internal/value	[no test files]
?   	github.com/influxdata/tdigest	[no test files]
?   	github.com/josharian/intern	[no test files]
?   	github.com/mailru/easyjson	[no test files]
?   	github.com/mailru/easyjson/buffer	[no test files]
?   	github.com/mailru/easyjson/jlexer	[no test files]
?   	github.com/mailru/easyjson/jwriter	[no test files]
?   	github.com/matttproud/golang_protobuf_extensions/pbutil	[no test files]
?   	github.com/onsi/ginkgo/v2	[no test files]
?   	github.com/onsi/ginkgo/v2/config	[no test files]
?   	github.com/onsi/ginkgo/v2/formatter	[no test files]
?   	github.com/onsi/ginkgo/v2/internal	[no test files]
?   	github.com/onsi/ginkgo/v2/internal/global	[no test files]
?   	github.com/onsi/ginkgo/v2/internal/interrupt_handler	[no test files]
?   	github.com/onsi/gomega/internal	[no test files]
?   	github.com/onsi/gomega/internal/gutil	[no test files]
?   	github.com/onsi/gomega/matchers	[no test files]
?   	github.com/onsi/gomega/matchers/support/goraph/bipartitegraph	[no test files]
?   	github.com/onsi/gomega/matchers/support/goraph/edge	[no test files]
?   	github.com/onsi/gomega/matchers/support/goraph/node	[no test files]
?   	github.com/onsi/gomega/matchers/support/goraph/util	[no test files]
?   	github.com/onsi/ginkgo/v2/types	[no test files]
?   	github.com/onsi/gomega/types	[no test files]
?   	github.com/prometheus/client_golang/prometheus	[no test files]
?   	github.com/prometheus/client_golang/prometheus/promhttp	[no test files]
?   	github.com/prometheus/client_golang/prometheus/testutil	[no test files]
?   	github.com/prometheus/client_golang/prometheus/testutil/promlint	[no test files]
?   	github.com/prometheus/client_golang/prometheus/internal	[no test files]
?   	github.com/prometheus/common/expfmt	[no test files]
?   	github.com/onsi/ginkgo/v2/internal/parallel_support	[no test files]
?   	github.com/onsi/ginkgo/v2/reporters	[no test files]
?   	github.com/prometheus/client_model/go	[no test files]
?   	github.com/onsi/ginkgo/v2/internal/testingtproxy	[no test files]
?   	github.com/onsi/gomega/ghttp	[no test files]
?   	github.com/prometheus/common/model	[no test files]
?   	github.com/prometheus/procfs	[no test files]
?   	github.com/prometheus/procfs/internal/fs	[no test files]
?   	github.com/onsi/gomega/format	[no test files]
?   	github.com/onsi/gomega	[no test files]
?   	github.com/prometheus/procfs/internal/util	[no test files]
?   	github.com/prometheus/common/internal/bitbucket.org/ww/goautoneg	[no test files]
?   	github.com/tsenart/vegeta/v12/lib	[no test files]
?   	github.com/rs/dnscache	[no test files]
?   	go/internal/typeparams	[no test files]
?   	golang.org/x/net/context	[no test files]
?   	golang.org/x/net/html	[no test files]
?   	golang.org/x/net/html/atom	[no test files]
?   	golang.org/x/net/html/charset	[no test files]
?   	golang.org/x/net/http/httpguts	[no test files]
?   	golang.org/x/net/http2	[no test files]
?   	golang.org/x/net/http2/hpack	[no test files]
?   	golang.org/x/net/idna	[no test files]
?   	golang.org/x/sync/singleflight	[no test files]
?   	golang.org/x/sys/execabs	[no test files]
?   	golang.org/x/sys/unix	[no test files]
?   	golang.org/x/text/cases	[no test files]
?   	golang.org/x/text/encoding	[no test files]
?   	golang.org/x/text/encoding/charmap	[no test files]
?   	golang.org/x/text/encoding/htmlindex	[no test files]
?   	golang.org/x/text/encoding/internal	[no test files]
?   	golang.org/x/text/encoding/internal/identifier	[no test files]
?   	golang.org/x/text/encoding/japanese	[no test files]
?   	golang.org/x/text/encoding/korean	[no test files]
?   	golang.org/x/text/encoding/simplifiedchinese	[no test files]
?   	golang.org/x/text/encoding/traditionalchinese	[no test files]
?   	golang.org/x/text/encoding/unicode	[no test files]
?   	golang.org/x/text/internal	[no test files]
?   	golang.org/x/text/internal/language	[no test files]
?   	golang.org/x/text/internal/language/compact	[no test files]
?   	golang.org/x/text/internal/tag	[no test files]
?   	golang.org/x/text/internal/utf8internal	[no test files]
?   	golang.org/x/text/language	[no test files]
?   	golang.org/x/text/runes	[no test files]
?   	golang.org/x/text/secure/bidirule	[no test files]
?   	golang.org/x/text/transform	[no test files]
?   	golang.org/x/text/unicode/bidi	[no test files]
?   	golang.org/x/text/unicode/norm	[no test files]
?   	google.golang.org/protobuf/encoding/prototext	[no test files]
?   	google.golang.org/protobuf/internal/encoding/defval	[no test files]
?   	google.golang.org/protobuf/internal/encoding/messageset	[no test files]
?   	google.golang.org/protobuf/internal/encoding/tag	[no test files]
?   	google.golang.org/protobuf/internal/encoding/text	[no test files]
?   	google.golang.org/protobuf/internal/errors	[no test files]
?   	google.golang.org/protobuf/internal/descopts	[no test files]
?   	google.golang.org/protobuf/internal/filetype	[no test files]
?   	google.golang.org/protobuf/internal/flags	[no test files]
?   	google.golang.org/protobuf/internal/genid	[no test files]
?   	google.golang.org/protobuf/internal/detrand	[no test files]
?   	google.golang.org/protobuf/internal/impl	[no test files]
?   	google.golang.org/protobuf/internal/set	[no test files]
?   	google.golang.org/protobuf/internal/strs	[no test files]
?   	google.golang.org/protobuf/internal/version	[no test files]
?   	google.golang.org/protobuf/proto	[no test files]
?   	google.golang.org/protobuf/encoding/protowire	[no test files]
?   	google.golang.org/protobuf/reflect/protodesc	[no test files]
?   	google.golang.org/protobuf/internal/order	[no test files]
?   	google.golang.org/protobuf/reflect/protoreflect	[no test files]
?   	google.golang.org/protobuf/internal/descfmt	[no test files]
?   	google.golang.org/protobuf/internal/pragma	[no test files]
?   	google.golang.org/protobuf/reflect/protoregistry	[no test files]
?   	google.golang.org/protobuf/runtime/protoiface	[no test files]
?   	google.golang.org/protobuf/internal/filedesc	[no test files]
?   	google.golang.org/protobuf/runtime/protoimpl	[no test files]
?   	google.golang.org/protobuf/types/descriptorpb	[no test files]
?   	google.golang.org/protobuf/types/known/timestamppb	[no test files]
?   	gopkg.in/yaml.v3	[no test files]
?   	internal/bisect	[no test files]
?   	internal/bytealg	[no test files]
?   	internal/coverage/rtcov	[no test files]
?   	internal/goarch	[no test files]
?   	internal/goexperiment	[no test files]
?   	internal/goos	[no test files]
?   	internal/goroot	[no test files]
?   	internal/goversion	[no test files]
?   	internal/lazyregexp	[no test files]
?   	internal/nettrace	[no test files]
?   	internal/oserror	[no test files]
?   	internal/race	[no test files]
?   	internal/syscall/execenv	[no test files]
?   	internal/syscall/unix	[no test files]
?   	internal/sysinfo	[no test files]
?   	internal/testlog	[no test files]
?   	log/internal	[no test files]
?   	net/http/internal/testcert	[no test files]
?   	unsafe	[no test files]
?   	vendor/golang.org/x/crypto/chacha20	[no test files]
?   	vendor/golang.org/x/crypto/chacha20poly1305	[no test files]
?   	vendor/golang.org/x/crypto/cryptobyte	[no test files]
?   	vendor/golang.org/x/crypto/cryptobyte/asn1	[no test files]
?   	vendor/golang.org/x/crypto/hkdf	[no test files]
?   	vendor/golang.org/x/crypto/internal/alias	[no test files]
?   	vendor/golang.org/x/crypto/internal/poly1305	[no test files]
?   	vendor/golang.org/x/net/dns/dnsmessage	[no test files]
?   	vendor/golang.org/x/net/http/httpguts	[no test files]
?   	vendor/golang.org/x/net/http/httpproxy	[no test files]
?   	vendor/golang.org/x/net/idna	[no test files]
?   	vendor/golang.org/x/net/http2/hpack	[no test files]
?   	vendor/golang.org/x/net/route	[no test files]
?   	vendor/golang.org/x/text/secure/bidirule	[no test files]
?   	vendor/golang.org/x/text/unicode/bidi	[no test files]
?   	vendor/golang.org/x/text/unicode/norm	[no test files]
?   	vendor/golang.org/x/text/transform	[no test files]
ok  	github.com/alphagov/router/handlers	10.777s
ok  	github.com/alphagov/router/integration_tests	72.213s
ok  	github.com/alphagov/router/lib	(cached)
ok  	github.com/alphagov/router/trie	(cached)
ok  	github.com/alphagov/router/triemux	(cached)
ok  	go/ast	(cached)
ok  	go/build	(cached)
ok  	go/build/constraint	(cached)
ok  	go/doc	(cached)
ok  	go/doc/comment	(cached)
ok  	go/parser	(cached)
ok  	go/scanner	(cached)
ok  	go/token	(cached)
ok  	hash	(cached)
ok  	hash/crc32	(cached)
ok  	hash/fnv	(cached)
ok  	html	(cached)
ok  	html/template	(cached)
ok  	internal/abi	(cached)
ok  	internal/buildcfg	(cached)
ok  	internal/cpu	(cached)
ok  	internal/fmtsort	(cached)
ok  	internal/godebug	(cached)
ok  	internal/godebugs	(cached)
ok  	internal/intern	(cached)
ok  	internal/itoa	(cached)
ok  	internal/platform	(cached)
ok  	internal/poll	(cached)
ok  	internal/reflectlite	(cached)
ok  	internal/safefilepath	(cached)
ok  	internal/saferio	(cached)
ok  	internal/singleflight	(cached)
ok  	internal/unsafeheader	(cached)
ok  	io	(cached)
ok  	io/fs	(cached)
ok  	io/ioutil	(cached)
ok  	log	(cached)
ok  	math	(cached)
ok  	math/big	(cached)
ok  	math/bits	(cached)
ok  	math/rand	(cached)
ok  	mime	(cached)
ok  	mime/multipart	(cached)
ok  	mime/quotedprintable	(cached)
ok  	net	(cached)
ok  	net/http	(cached)
ok  	net/http/httptest	(cached)
ok  	net/http/httptrace	(cached)
ok  	net/http/httputil	(cached)
ok  	net/http/internal	(cached)
ok  	net/http/internal/ascii	(cached)
ok  	net/netip	(cached)
ok  	net/rpc	(cached)
ok  	net/textproto	(cached)
ok  	net/url	(cached)
ok  	os	17.063s
ok  	os/exec	(cached)
ok  	os/signal	(cached)
ok  	path	(cached)
ok  	path/filepath	(cached)
ok  	reflect	(cached)
ok  	regexp	(cached)
ok  	regexp/syntax	(cached)
ok  	runtime	(cached)
ok  	runtime/debug	(cached)
ok  	runtime/internal/atomic	(cached)
ok  	runtime/internal/math	(cached)
ok  	runtime/internal/sys	(cached)
ok  	runtime/metrics	(cached)
ok  	runtime/trace	(cached)
ok  	sort	(cached)
ok  	strconv	(cached)
ok  	strings	(cached)
ok  	sync	(cached)
ok  	sync/atomic	(cached)
ok  	syscall	(cached)
ok  	testing	(cached)
ok  	text/tabwriter	(cached)
ok  	text/template	(cached)
ok  	text/template/parse	(cached)
ok  	time	(cached)
ok  	unicode	(cached)
ok  	unicode/utf16	(cached)
ok  	unicode/utf8	(cached)
FAIL

[ChrisBAshton]

LGTM 👍 one nitpick below