Update codecov action.

Author: luciansmith

.github/workflows/ci.yml

@@ -148,7 +148,7 @@ jobs:
         run: python -m pytest tests/ --cov=biosimulators_tellurium --cov-report=xml
 
       - name: Upload the coverage report to Codecov
-        uses: codecov/codecov-action@v3
+        uses: codecov/codecov-action@v4
         with:
           token: ${{ secrets.CODECOV_TOKEN }}
           flags: unittests