Fix a ruby warning when executing with `bundle exec rubocop` in this repository

[Earlopain]

check_commit.rake requires 'English' but when doing bundle exec rubocop this repository this file will also be evaluated.

This also happens in the rubocop repository (my main motivation here) if rubocop-ast is in the parent folder because of this line in its Gemfile: https://github.com/rubocop/rubocop/blob/66c8276b5d9e60fed1fb8d937649c3c153e5037d/Gemfile#L29-L30

$ RUBYOPT=-w bundle exec rubocop -V
.../rubocop-ast/rubocop-ast.gemspec:18: warning: global variable `$RS' not initialized
1.62.1 (using Parser 3.3.0.5, rubocop-ast 1.31.2, running on ruby 3.3.0) [x86_64-linux]
  - rubocop-performance 1.20.2
  - rubocop-rspec 2.27.1

[koic]

Can you update to another approach that avoids using $RS in s.files= of the rubocop-ast gemspec, instead of requiring English?

[Earlopain]

Yeah, sure. Updated