CI: Update codecov action to version 4

* Update codecov/codecov-action from version 3 to version 4.
* The new version provides better reliability and performance.

Author: ityaozm@gmail.com

.github/workflows/tests.yml

@@ -38,7 +38,7 @@ jobs:
         run: composer test-c
 
       - name: Upload coverage to Codecov
-        uses: codecov/codecov-action@v3
+        uses: codecov/codecov-action@v4
         with:
           files: ./clover.xml
           token: ${{ secrets.CODECOV_TOKEN }} # not required for public repos