chore(deps): update codecov/codecov-action action to v6

Author: renovate[bot]

.github/workflows/ci.yml

@@ -64,7 +64,7 @@ jobs:
           make tests
       - name: Run code coverage
         if: matrix.python-version == '3.12' && matrix.django-version == 'django42'
-        uses: codecov/codecov-action@v5
+        uses: codecov/codecov-action@v6
         with:
           flags: unittests
           fail_ci_if_error: true