Update actions/checkout action to v4

Author: renovate[bot]

.github/workflows/main.yml

@@ -7,7 +7,7 @@ jobs:
   python-code-format:
     runs-on: ubuntu-24.04
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - uses: actions/setup-python@v4
         with:
           python-version: "3.10"