Update rubocop requirement from ~> 1.77.0 to ~> 1.78.0 (#270)

Updates the requirements on [rubocop](https://github.com/rubocop/rubocop) to permit the latest version.
- [Release notes](https://github.com/rubocop/rubocop/releases)
- [Changelog](https://github.com/rubocop/rubocop/blob/master/CHANGELOG.md)
- [Commits](rubocop/rubocop@v1.77.0...v1.78.0)

---
updated-dependencies:
- dependency-name: rubocop
  dependency-version: 1.78.0
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

pygments.rb.gemspec

@@ -25,7 +25,7 @@ Gem::Specification.new do |s|
   s.required_ruby_version = '>= 2.7.0'
 
   s.add_development_dependency 'rake', '~> 13.3.0'
-  s.add_development_dependency 'rubocop', '~> 1.77.0'
+  s.add_development_dependency 'rubocop', '~> 1.78.0'
   s.add_development_dependency 'test-unit', '~> 3.7.0'
 
   s.files = `git ls-files -z`.split("\0").reject { |f| File.symlink?(f) }