chore: async artifact image cleanup (#56)

Author: Pigbibi

.github/workflows/sync-cloud-run-env.yml

@@ -596,5 +596,6 @@ jobs:
             gcloud artifacts docker images delete "${image_repo}@${digest}" \
               --project="${GCP_PROJECT_ID}" \
               --delete-tags \
+              --async \
               --quiet
           done <<< "${old_digests}"