Update actions cache

Author: tudoramariei

.github/workflows/backend_check.yml

@@ -37,7 +37,7 @@ jobs:
         cache: 'pip'
 
     - name: Cache pip
-      uses: actions/cache@v3
+      uses: actions/cache@v4
       with:
         path: ~/.cache/pip
         key: ${{ runner.os }}-pip-${{ hashFiles('**/requirements-dev.txt') }}