.github: Bump actions/checkout to v4

.github/workflows/compile.yml

@@ -13,7 +13,7 @@ jobs:
   build:
     runs-on: [ubuntu-latest]
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Basic checks
       run: pip install pre-commit && pre-commit run --all-files --show-diff-on-failure --color=always
     - name: Install latex