Update rubocop-govuk requirement from = 4.18.0 to = 5.0.1

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@v4.18.0...v5.0.1)

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

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

govuk_admin_template.gemspec

@@ -24,6 +24,6 @@ Gem::Specification.new do |gem|
   gem.add_development_dependency "capybara", "~> 3"
   gem.add_development_dependency "climate_control", "~> 1"
   gem.add_development_dependency "rspec-rails", "~> 5"
-  gem.add_development_dependency "rubocop-govuk", "4.18.0"
+  gem.add_development_dependency "rubocop-govuk", "5.0.1"
   gem.add_development_dependency "sassc-rails", "~> 2"
 end