Bump rubocop-govuk from 3.14.0 to 3.15.0
Bump rubocop-govuk from 3.14.0 to 3.15.0

Bumps [rubocop-govuk](https://github.com/alphagov/rubocop-govuk) from 3.14.0 to 3.15.0.
- [Release notes](https://github.com/alphagov/rubocop-govuk/releases)
- [Changelog](https://github.com/alphagov/rubocop-govuk/blob/master/CHANGELOG.md)
- [Commits](https://github.com/alphagov/rubocop-govuk/compare/v3.14.0...v3.15.0)

Signed-off-by: dependabot-preview[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
alphagov/publishing-api,alphagov/publishing-api