Bump actions/checkout to v4 in CI

Author: flashcode

.github/workflows/ci.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-22.04
     name: Check scripts
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: Set up Python
         uses: actions/setup-python@v2
         with: