Skip build-and-push on pull_request events

The build-and-push job was running on PRs and trying to log in to the
Gitea Container Registry, which always fails on PRs because the
github.token has no package write permission. Add if:
github.event_name == 'push' so the job is skipped for PRs and the
overall run can stay green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -89,6 +89,7 @@ jobs:
         run: pytest --tb=short -q
 
   build-and-push:
+    if: github.event_name == 'push'
     runs-on: ubuntu-latest
     needs: [lint, test]
     outputs: