ci(docker): fix attestation (#54)

Author: matteo-cristino

.github/workflows/release.yaml

@@ -93,6 +93,7 @@ jobs:
 
       - name: Build and push Docker image
         uses: docker/build-push-action@v5
+        id: push
         with:
           context: .
           push: true
@@ -107,5 +108,5 @@ jobs:
         uses: actions/attest-build-provenance@v3
         with:
           subject-name: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
-          subject-digest: ${{ steps.build.outputs.digest }}
+          subject-digest: ${{ steps.push.outputs.digest }}
           push-to-registry: true