Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/run-tests.yaml

@@ -16,7 +16,7 @@ jobs:
 
     steps:
       - name: Git checkout
-        uses: "actions/checkout@v4.2.2"
+        uses: "actions/checkout@v6.0.0"
 
       - name: Set up Python ${{ matrix.py_version }}
         uses: actions/setup-python@v5.6.0