ci: 👷 upgrade codecov-action to v4

Author: HofmannZ

.github/workflows/ci.yml

@@ -83,6 +83,6 @@ jobs:
             --coverage
 
       - name: Upload code coverage
-        uses: codecov/codecov-action@v3
+        uses: codecov/codecov-action@v4
         with:
           token: ${{ secrets.CODECOV_TOKEN }}