🐳 fix build attestation (#267)

This PR fixes a small error in the build attestation job where the name
was left empty.

.github/workflows/docker.yml

@@ -11,6 +11,10 @@ on:
     branches:
       - "main"
 
+env:
+  REGISTRY: docker.io
+  IMAGE_NAME: burgholzer/mqt-ddvis
+
 jobs:
   push_to_registry:
     name: Push Docker image to Docker Hub
@@ -37,7 +41,7 @@ jobs:
         id: meta
         uses: docker/metadata-action@v5
         with:
-          images: burgholzer/mqt-ddvis
+          images: ${{ env.IMAGE_NAME }}
 
       - name: Build and push Docker image
         id: push
@@ -49,8 +53,9 @@ jobs:
           labels: ${{ steps.meta.outputs.labels }}
 
       - name: Generate artifact attestation
+        if: ${{ github.event_name != 'pull_request' }}
         uses: actions/attest-build-provenance@v1
         with:
           subject-name: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME}}
           subject-digest: ${{ steps.push.outputs.digest }}
-          push-to-registry: ${{ github.event_name != 'pull_request' }}
+          push-to-registry: true