ci: fail stale backend golden image checks

.gitea/workflows/ci-cd.yml

@@ -109,6 +109,7 @@ jobs:
           image_usable() {
             docker run --rm "${CI_GOLDEN_REF}:${GOLDEN_TAG}" \
               bash -c "
+                set -euo pipefail
                 test -f /app/uv.lock
                 test \"\$(sha256sum /app/uv.lock | awk '{ print \$1 }')\" = '${lockfile_sha}'
                 /app/.venv/bin/ruff --version >/dev/null