fix: using pull_request.head.sha for checkout on PR events

Author: dlactin

.github/workflows/build-and-push-images.yaml

@@ -35,6 +35,7 @@ jobs:
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
         with:
           fetch-tags: true
+          ref: ${{ github.event_name == 'pull_request' && github.event.pull_request.head.sha || github.ref }}
       - uses: docker/setup-buildx-action@b5ca514318bd6ebac0fb2aedd5d36ec1b5c232a2
       - id: gcp-auth
         name: Google authentication