CI: Fix git repo ref in format-check workflow (#37563)

Author: aaronsteers

.github/workflows/format_check.yml

@@ -104,6 +104,7 @@ jobs:
         uses: actions/checkout@v4
         with:
           ref: ${{ github.event.pull_request.head.ref }}
+          repository: ${{ github.event.pull_request.head.repo.full_name }}
           fetch-depth: 1
       - name: Set up Python
         uses: actions/setup-python@v5