fix(ci): dereference annotated tags in hotfix validation

Use ^{commit} to get the commit SHA from annotated tags, otherwise
git rev-parse returns the tag object SHA which causes comparison failures.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: julienld

.github/workflows/pr-validate-hotfix.yml

@@ -33,7 +33,8 @@ jobs:
             exit 0
           fi
 
-          STABLE_COMMIT=$(git rev-parse stable)
+          # Use ^{commit} to dereference annotated tags to the commit SHA
+          STABLE_COMMIT=$(git rev-parse stable^{commit})
           STABLE_TAG_NAME=$(git describe --tags --exact-match $STABLE_COMMIT 2>/dev/null || echo "stable")
           echo "Stable tag points to: $STABLE_TAG_NAME ($STABLE_COMMIT)"