tools/update-oss.sh: check against GitHub instead of a local clone

tools/update-oss.sh

@@ -3,14 +3,17 @@
 # Usage: update-oss.sh <directory-path>
 #
 # Update the version of the tailscale.com module to be in sync with the version
-# used by the repo checked out in the specified directory.
+# used by the specified repository.
 #
-# Requires: git, go, jq
+# Requires: gh, git, go, jq
 #
 set -euo pipefail
 
 # The repository path to compare to.
-repo="${1:?missing repository path}"
+repo=tailscale/corp
+
+# The module to update.
+module=tailscale.com
 
 cd "$(dirname ${BASH_SOURCE[0]})/.."
 if ! git diff --quiet ; then
@@ -21,23 +24,17 @@ if ! git diff --quiet ; then
 fi
 git checkout --quiet main && git pull --rebase --quiet
 
-# The module to update.
-module=tailscale.com
-
-# The branch name to use when making an update.
-branch="$USER"/update-oss-version
-
 have="$(go list -f '{{.Version}}' -m "$module" | cut -d- -f3)"
-want="$(cd "$repo";  go list -f '{{.Version}}' -m "$module" |  cut -d- -f3)"
+want="$(
+  gh api -q '.content|@base64d' repos/"${repo}"/contents/go.mod |
+  grep -E "\b${module}\b" | cut -d' ' -f2 | cut -d- -f3
+)"
 if [[ "$have" = "$want" ]] ; then
     echo "Module $module is up-to-date at commit $have" 1>&2
     exit 0
 fi
 
 go get "$module"@"$want"
 go mod tidy
-git checkout -b "$branch"
-git commit -m "go.mod: update $module to commit $want" go.mod go.sum
-git push -u origin "$branch"
 echo "Module $module updated to commit $want" 1>&2
-echo "Branch $branch created" 1>&2
+echo "(you must commit and push this change to persist it)" 1>&2