Fix checkout ref to use HEAD_BRANCH environment variable

Author: nixel2007

.github/workflows/qa.yml

@@ -35,9 +35,11 @@ jobs:
       env:
         GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
     - uses: actions/checkout@v6
+      env:
+        HEAD_BRANCH: ${{ github.event.workflow_run.head_branch }}
       with:
           repository: ${{ github.event.workflow_run.head_repository.full_name }}
-          ref: ${{ github.event.workflow_run.head_branch }}
+          ref: "$HEAD_BRANCH"
           fetch-depth: 0
     - name: Checkout base branch
       if: github.event.workflow_run.event == 'pull_request'