github: limit container push action

Only push the container to ghcr in case the repository is owned by the
freifunk-gluon organization.

THis avoids failing CI on forks.

Signed-off-by: David Bauer <mail@david-bauer.net>

.github/workflows/build-container.yml

@@ -21,6 +21,7 @@ jobs:
         uses: actions/checkout@v4
       - name: Log in to the Container registry
         uses: docker/login-action@b4bedf8053341df3b5a9f9e0f2cf4e79e27360c6
+        if: ${{ github.repository_owner == 'freifunk-gluon' }}
         with:
           registry: ${{ env.REGISTRY }}
           username: ${{ github.actor }}
@@ -34,6 +35,6 @@ jobs:
         uses: docker/build-push-action@4c1b68d83ad20cc1a09620ca477d5bbbb5fa14d0
         with:
           context: ./contrib/docker
-          push: true
+          push: ${{ github.repository_owner == 'freifunk-gluon' }}
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}