tools: Handle v-prefixed versions in stable-tag.sh (#28455)

If the GH version tag has the "v" prefix, that should be stripped before
comparing it with the SVN version and readme versions.

tools/stable-tag.sh

@@ -105,7 +105,7 @@ if ! jq -e '.' <<<"$JSON" &>/dev/null; then
 	die "Failed to retrieve JSON data from https://api.github.com/repos/$MIRROR/releases/latest"
 fi
 
-GH_LATEST=$(jq -r '.tag_name' <<<"$GH_JSON")
+GH_LATEST=$(jq -r '.tag_name | ltrimstr( "v" )' <<<"$GH_JSON")
 
 yellow "Current stable tag: ${CURRENT_STABLE_VERSION}"
 yellow "Latest tag in SVN: ${SVN_LATEST}"