Update actions/checkout

Author: CJLove

.github/workflows/ci.yml

@@ -22,7 +22,7 @@ jobs:
       image: ${{ matrix.config.compiler == 'clang' && 'teeks99/clang-ubuntu' || matrix.config.compiler }}:${{ matrix.config.version }}
     name: "${{ matrix.config.compiler}} ${{ matrix.config.version }} (C++${{ matrix.config.cppstd }}, ${{ matrix.config.build_type }})"
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: Setup
         run: |
           apt-get update && apt-get install -y curl git