ci: bump codecov/codecov-action from 4 to 6

Bumps [codecov/codecov-action](https://github.com/codecov/codecov-action) from 4 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@v4...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/ci.yml

@@ -38,7 +38,7 @@ jobs:
 
       - name: Upload coverage
         if: matrix.python-version == '3.13'
-        uses: codecov/codecov-action@v4
+        uses: codecov/codecov-action@v6
         with:
           file: coverage.xml
           fail_ci_if_error: false