Woops, attestation subject === image name for #656

I re-read the dogs. Attestations will be uploaded to Sigstore but I will
not busy up the registry with them every moment as it will make it even
more confusing for novice users and advanced developers what data they
are looking for by content-addressable git commit hash ID.

.github/workflows/content-artifacts.yml

@@ -115,6 +115,5 @@ jobs:
       - name: Container image push attestations
         uses: actions/attest-build-provenance@1c608d11d69870c2092266b3f9a6f3abbf17002c
         with:
-          subject-name: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME}}-attestation
+          subject-name: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME}}
           subject-digest: ${{ steps.image_registry_push.outputs.digest }}
-          push-to-registry: true