Support dtls 1.3 downgrade mechanism #117

Job	Run time
check-ansi	2m 39s
address_ub_sanitizer	1m 4s
basic_clang	1m 19s
basic_gcc	1m 5s
check_docs	56s
check_update	1m 11s
fuzz_tests	59s
memory_sanitizer	1m 41s
minimal	42s
no-deprecated	1m 11s
non-caching	1m 2s
no-shared-macos	2m 23s
no-shared-ubuntu	1m 6s
self-hosted (freebsd-13.2)	1s
self-hosted (ubuntu-arm64-22.04)	1s
enable_non-default_options	1m 1s
external-test-cf-quiche	1m 44s
external-test-pyca (1.51.0, 3.9)	1m 18s
external-tests	1m 30s
full_featured	1m 12s
legacy	49s
no-legacy	1m 8s
out-of-readonly-source-and-install-macos	2m 24s
out-of-readonly-source-and-install-ubuntu	1m 4s
threads_sanitizer	1m 24s
	30m 54s

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