RuboCop: Make comments in inline disables consistent

What does this MR do and why?

Use "--" as suggested in https://docs.gitlab.com/ee/development/rubocop_development_guide.html#disabling-rules-inline

Helps with #428749 (closed) and anticipates changes in !134663 (merged).

Note that Danger did not comment on any instance of rubocop:disable which is intended because all inline disable have a properly formatted comment. See !134663 (merged).

How to set up and validate locally

bundle exec rubocop $(git diff --name-only HEAD~)

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.