Ensure hub username is set when publishing in GHA workflow

Author: mikesir87

.github/workflows/deploy-labspace-compose.yaml

@@ -28,3 +28,5 @@ jobs:
       - name: Publish Compose file
         run: |
           docker compose -f oci://dockersamples/labspace -f .labspace/compose.override.yaml publish $DOCKERHUB_USERNAME/labspace-container-supported-development --with-env -y
+        env:
+          DOCKERHUB_USERNAME: ${{ secrets.DOCKERHUB_USERNAME }}