Bump rubocop from 1.20.0 to 1.21.0 (#16733)

Bump rubocop from 1.20.0 to 1.21.0 (#16733)

Bumps [rubocop](https://github.com/rubocop/rubocop) from 1.20.0 to 1.21.0.
- [Release notes](https://github.com/rubocop/rubocop/releases)
- [Changelog](https://github.com/rubocop/rubocop/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rubocop/rubocop/compare/v1.20.0...v1.21.0)

---
updated-dependencies:
- dependency-name: rubocop
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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