Bump rubocop-rails from 2.5.2 to 2.6.0 (#14047)

Bump rubocop-rails from 2.5.2 to 2.6.0 (#14047)

Bumps [rubocop-rails](https://github.com/rubocop-hq/rubocop-rails) from 2.5.2 to 2.6.0.
- [Release notes](https://github.com/rubocop-hq/rubocop-rails/releases)
- [Changelog](https://github.com/rubocop-hq/rubocop-rails/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rubocop-hq/rubocop-rails/compare/v2.5.2...v2.6.0)

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