Update checkout action to v6

Author: fabaff

.github/workflows/python.yml

@@ -15,7 +15,7 @@ jobs:
         python-version: [ "3.13", "3.14" ]
 
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
     - name: Set up Python ${{ matrix.python-version }}
       uses: actions/setup-python@v5
       with: