Merge pull request #102 from svengo/feature/multiple-attestations

- New Features
  - Consolidated Docker image attestation steps for improved efficiency.
  - Updated attestation to support multiple image names in a single entry.

- Bug Fixes
  - Adjusted input indentation for the subject-name to accommodate multi-line format.

.github/workflows/publish-docker.yml

@@ -76,17 +76,12 @@ jobs:
         cache-to: type=gha,mode=max
         platforms: linux/amd64
     -
-      name: Attest DockerHub
+      name: Attest Docker images
       uses: actions/attest-build-provenance@v2
       with:
-        subject-name: docker.io/${{ vars.DOCKERHUB_USERNAME }}/${{ vars.IMAGE_NAME }}
-        subject-digest: ${{ steps.push.outputs.digest }}
-        push-to-registry: true
-    -
-      name: Attest ghcr
-      uses: actions/attest-build-provenance@v2
-      with:
-        subject-name: ghcr.io/${{ github.repository_owner }}/${{ vars.IMAGE_NAME }}
+        subject-name: |
+          docker.io/${{ vars.DOCKERHUB_USERNAME }}/${{ vars.IMAGE_NAME }}
+          ghcr.io/${{ github.repository_owner }}/${{ vars.IMAGE_NAME }}
         subject-digest: ${{ steps.push.outputs.digest }}
         push-to-registry: true
     -