Pin version of ruamel.yaml to avoid checks breaking

.github/workflows/pr-checks.yml

@@ -47,12 +47,12 @@ jobs:
       - name: Set up Python
         uses: actions/setup-python@v4
         with:
-          python-version: 3.8
+          python-version: 3.11
 
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
-          pip install ruamel.yaml
+          pip install ruamel.yaml==0.17.31
 
       # Ensure the generated PR check workflows are up to date.
       - name: Verify PR checks up to date