Update checkout action to fix deprecation warnings

.github/workflows/ci.yml

@@ -39,7 +39,7 @@ jobs:
       run: sudo apt-get update && sudo apt-get install libxrandr-dev libxcursor-dev libudev-dev libopenal-dev libflac-dev libvorbis-dev libgl1-mesa-dev libegl1-mesa-dev
 
     - name: Checkout SFML
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
       with:
         repository: SFML/SFML
         ref: 2.6.0
@@ -54,7 +54,7 @@ jobs:
       run: cmake --build $GITHUB_WORKSPACE/SFML/build --config ${{matrix.type.name}} --target install
 
     - name: Checkout CSFML
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
       with:
         path: CSFML