⬆️ bump codecov/codecov-action from 5.5.2 to 6.0.0 (#377)

Bumps [codecov/codecov-action](https://github.com/codecov/codecov-action) from 5.5.2 to 6.0.0.
- [Release notes](https://github.com/codecov/codecov-action/releases)
- [Changelog](https://github.com/codecov/codecov-action/blob/main/CHANGELOG.md)
- [Commits](codecov/codecov-action@v5.5.2...v6.0.0)

---
updated-dependencies:
- dependency-name: codecov/codecov-action
  dependency-version: 6.0.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/tests.yml

@@ -49,7 +49,7 @@ jobs:
 
     - name: Upload to Codecov
       if: matrix.os == 'ubuntu-latest' && matrix.python-version == '3.13' && github.repository == 'QuantEcon/quantecon-book-theme' && github.event_name == 'pull_request'
-      uses: codecov/codecov-action@v5.5.2
+      uses: codecov/codecov-action@v6.0.0
       with:
         name: ebp-qbt-pytests-py3.13
         flags: pytests