Update rubocop-govuk requirement from = 4.11.0 to = 4.12.0

Updates the requirements on [rubocop-govuk](https://github.com/alphagov/rubocop-govuk) to permit the latest version.
- [Changelog](https://github.com/alphagov/rubocop-govuk/blob/main/CHANGELOG.md)
- [Commits](alphagov/rubocop-govuk@v4.11.0...v4.12.0)

---
updated-dependencies:
- dependency-name: rubocop-govuk
  dependency-type: direct:development
...

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

govuk_personalisation.gemspec

@@ -33,5 +33,5 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency "pry-byebug"
   spec.add_development_dependency "rake"
   spec.add_development_dependency "rspec-rails"
-  spec.add_development_dependency "rubocop-govuk", "4.11.0"
+  spec.add_development_dependency "rubocop-govuk", "4.12.0"
 end