Bump VERSION to 6.1.0

• Diff: https://gitlab.com/gitlab-org/gitlab-styles/-/compare/v6.0.0...073cc6f1dc8f665477fc35821a47712f1a4c9a54

• Release notes:

### New features and features updates

- !72 Add cop `Style/HashTransformation`.
- !71 CodeReuse rule: allow `limit`.
- !73 Support `TargetRubyVersion` 3.0.

• Checklist before merging:

  • Diff link is up-to-date.
  • Based on the diff, lib/gitlab/styles/version.rb is updated, according to SemVer.
  • Release notes are accurate.

• Checklist after merging:

  • Update the release notes for the newly created tag.

Closes #17 (closed)