Update codecov/codecov-action action to v4

| datasource  | package                | from | to |
| ----------- | ---------------------- | ---- | -- |
| github-tags | codecov/codecov-action | v3   | v4 |

.github/workflows/continuous-integration.yaml

@@ -49,7 +49,7 @@ jobs:
         run: "vendor/bin/phpunit --coverage-clover coverage.xml"
 
       - name: "upload to codecov"
-        uses: codecov/codecov-action@v3
+        uses: codecov/codecov-action@v4
 
   mutation-tests:
     name: "mutation tests"