build(deps-dev): bump libcst from 1.5.1 to 1.6.0

Bumps [libcst](https://github.com/Instagram/LibCST) from 1.5.1 to 1.6.0.
- [Release notes](https://github.com/Instagram/LibCST/releases)
- [Changelog](https://github.com/Instagram/LibCST/blob/main/CHANGELOG.md)
- [Commits](Instagram/LibCST@v1.5.1...v1.6.0)

---
updated-dependencies:
- dependency-name: libcst
  dependency-type: indirect
  update-type: version-update:semver-minor
...

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