fix: fix CI that want to push on PR

Author: jeffpeng3

.github/workflows/build.yaml

@@ -34,7 +34,7 @@ jobs:
 
       - uses: docker/build-push-action@v6
         with:
-          push: ${{ github.event_name != 'pull_request' }}
+          push: ${{ github.ref == 'refs/heads/main' && github.event_name == 'push' }}
           context: .
           tags: ${{ steps.metadata.outputs.tags }}
           labels: ${{ steps.metadata.outputs.labels }}