Fix tag name?

Author: sourcefrog

.github/workflows/container.yml

@@ -46,7 +46,7 @@ jobs:
         id: push
         # --platform linux/amd64,linux/arm64
         run: |
-          docker build --push -t ${{ env.REGISTRY }}/${{ github.repository }}:${{ steps.meta.outputs.tags }} .
+          docker build --push -t ghcr.io/sourcefrog/cargo-mutants:container .
 
       # - name: Generate artifact attestation
       #   uses: actions/attest-build-provenance@v2