Update rubocop-rails requirement from = 2.27.0 to = 2.28.0

Updates the requirements on [rubocop-rails](https://github.com/rubocop/rubocop-rails) to permit the latest version.
- [Release notes](https://github.com/rubocop/rubocop-rails/releases)
- [Changelog](https://github.com/rubocop/rubocop-rails/blob/master/CHANGELOG.md)
- [Commits](rubocop/rubocop-rails@v2.27.0...v2.28.0)

---
updated-dependencies:
- dependency-name: rubocop-rails
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

rubocop-govuk.gemspec

@@ -18,7 +18,7 @@ Gem::Specification.new do |spec|
   spec.add_dependency "rubocop", "1.69.2"
   spec.add_dependency "rubocop-ast", "1.37.0"
   spec.add_dependency "rubocop-capybara", "2.21.0"
-  spec.add_dependency "rubocop-rails", "2.27.0"
+  spec.add_dependency "rubocop-rails", "2.28.0"
   spec.add_dependency "rubocop-rake", "0.6.0"
   spec.add_dependency "rubocop-rspec", "3.3.0"
 end