Moving CI to actions/checkout@v4 to remove deprecation warning

Author: whaeck

.github/workflows/ContinuousIntegration.yml

@@ -25,7 +25,7 @@ jobs:
       run: |
         which ${{matrix.cxx}}
         ${{matrix.cxx}} --version
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: mkdir bin
       run: mkdir bin
     - name: cmake