Update codecov/codecov-action action to v6

Author: renovate[bot]

.github/workflows/tests.yml

@@ -88,6 +88,6 @@ jobs:
           pip install pytest-cov
           pytest --cov=./
       - name: Upload coverage to Codecov
-        uses: codecov/codecov-action@v2
+        uses: codecov/codecov-action@v6
         with:
           name: codecov-umbrella