Update actions/setup-python action to v6

Author: renovate[bot]

.github/actions/format/action.yml

@@ -8,7 +8,7 @@ runs:
   using: 'composite'
   steps:
     - name: Set up Python
-      uses: actions/setup-python@v4
+      uses: actions/setup-python@v6
       with:
         python-version: '3.8'