ci: enhance Docker workflow to handle pull requests

Author: wei

.github/workflows/publish.yml

@@ -2,6 +2,7 @@ name: Create and publish a Docker image
 
 on:
   workflow_dispatch:
+  pull_request:
   push:
     branches:
       - "master"
@@ -42,11 +43,12 @@ jobs:
         uses: docker/build-push-action@v6
         with:
           context: .
-          push: true
+          push: ${{ github.event_name != 'pull_request' }}
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}
 
       - name: Generate artifact attestation
+        if: github.event_name != 'pull_request'
         uses: actions/attest-build-provenance@v2
         with:
           subject-name: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME}}