Allow Docker to build (but not push) on CI for PRs

Author: psychonic

.github/workflows/ci.yml

@@ -37,14 +37,14 @@ jobs:
     name: Build and push image
     runs-on: ubuntu-latest
     needs: [format, lint, type-check]
-    if: github.event_name == 'push' && github.ref == 'refs/heads/main'
     permissions:
       contents: read
       packages: write
     steps:
       - uses: actions/checkout@v6
 
       - name: Log in to GHCR
+        if: github.event_name == 'push' && github.ref == 'refs/heads/main'
         uses: docker/login-action@v4
         with:
           registry: ghcr.io
@@ -64,6 +64,6 @@ jobs:
         uses: docker/build-push-action@v7
         with:
           context: .
-          push: true
+          push: ${{ github.event_name == 'push' && github.ref == 'refs/heads/main' }}
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}