Background modal run so the runner exits quickly

modal run --detach keeps the CLI connected streaming logs; when the
GitHub Actions runner timeout fires it actively cancels the Modal app.
Background the command with & so the step exits after 10s and the
runner completes. --detach keeps the Modal app alive after the CLI
process is cleaned up.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: baogorek

.github/workflows/pipeline.yaml

@@ -55,4 +55,5 @@ jobs:
               ARGS="$ARGS --skip-national"
             fi
           fi
-          modal run --detach modal_app/pipeline.py::main $ARGS
+          modal run --detach modal_app/pipeline.py::main $ARGS &
+          sleep 10