Use cache@v4

.github/workflows/cpp.yml

@@ -42,7 +42,7 @@ jobs:
     steps:
       - uses: actions/checkout@v3
       - name: Cache dependencies
-        uses: actions/cache@v2
+        uses: actions/cache@v4
         with:
           path: ~/.apt/cache
           key: ${{ runner.os }}-apt-${{ hashFiles('**/ubuntu_dependencies.yml') }}