Bump gts from 3.1.1 to 6.0.2

Bumps [gts](https://github.com/google/gts) from 3.1.1 to 6.0.2.
- [Release notes](https://github.com/google/gts/releases)
- [Changelog](https://github.com/google/gts/blob/main/CHANGELOG.md)
- [Commits](https://github.com/google/gts/commits/v6.0.2)

---
updated-dependencies:
- dependency-name: gts
  dependency-version: 6.0.2
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]