ci: update codecov action

Author: alvarolopez

.github/workflows/codecov.yml

@@ -28,7 +28,7 @@ jobs:
         run: tox -e cov
 
       - name: Upload coverage to Codecov
-        uses: codecov/codecov-action@v3
+        uses: codecov/codecov-action@v4
         with:
           token: ${{ secrets.CODECOV_TOKEN }}
           fail_ci_if_error: true