build(deps): bump codecov/codecov-action from 5 to 6

Bumps [codecov/codecov-action](https://github.com/codecov/codecov-action) from 5 to 6.
- [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...v6)

---
updated-dependencies:
- dependency-name: codecov/codecov-action
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/test.yml

@@ -22,7 +22,7 @@ jobs:
       run: uv pip install --system -e .[test]
     - name: Test
       run: coverage run --source=./dpgen -m unittest -v && coverage report
-    - uses: codecov/codecov-action@v5
+    - uses: codecov/codecov-action@v6
       env:
         CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
       with: