Attempt to fix up lack of var.

.github/workflows/publish-docker-image.yaml

@@ -63,7 +63,7 @@ jobs:
       - name: Generate artifact attestation
         uses: actions/attest-build-provenance@v1
         with:
-          subject-name: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME}}
+          subject-name: ${{ env.REGISTRY }}/${{ github.repository }}
           subject-digest: ${{ steps.push.outputs.digest }}
           push-to-registry: true