chore: fix CI to run tests

Author: jacopo-chevallard

.github/workflows/backend-core-tests.yml

@@ -23,7 +23,7 @@ jobs:
         uses: actions/checkout@v2
 
       - name: Setup apt cache
-        uses: actions/cache@v2
+        uses: actions/cache@v4
         with:
           path: /var/cache/apt/archives
           key: ${{ runner.os }}-apt-${{ hashFiles('/etc/apt/sources.list') }}