chore(action): pin python and bump ct

Author: Frederic Spiers

.github/workflows/pull-request.yaml

@@ -30,10 +30,10 @@ jobs:
       - name: Set up Python
         uses: actions/setup-python@65d7f2d534ac1bc67fcd62888c5f4f3d2cb2b236 # v4.7.1
         with:
-          python-version: 3.x
+          python-version: 3.13
 
       - name: Set up chart-testing-action
-        uses: helm/chart-testing-action@v2.7.0
+        uses: helm/chart-testing-action@v2.8.0
 
       - name: Get changed charts
         id: list-changed