Refactor ci/deployable.rb to match Rubocop's style guide

What does this MR do and why?

It removes rubocop:disable comments and changes the code in the deployable.rb file to match Rubocop's style standards. I'm aiming to solve issue #420255.

How to set up and validate locally

1. Traverse to the gitlab folder
2. Rubocop the file: bundle exec rubocop app/models/concerns/ci/deployable.rb
3. Run testing suite to ensure changes didn't break anything. bundle exec rspec spec/models/concerns/ci/
4. Pipelines should pass

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.