RuboCop: Remove unnecessary cop disables for Rails/RakeEnvironment

What does this MR do and why?

This MR removes all inline 👮 disables of Rails/RakeEnvironment (which was disabled in !93419 (comment 1048223982)) to avoid flags by (currently disabled) 👮 Lint/RedundantCopDisableDirective.

Follow-up of !93419 (merged).

How to set up and validate locally

files="lib/tasks/contracts/merge_requests.rake lib/tasks/contracts/pipeline_schedules.rake lib/tasks/contracts/pipelines.rake lib/tasks/gems.rake lib/tasks/rubocop.rake qa/Rakefile qa/tasks/reliable_report.rake qa/tasks/vulnerabilities.rake"

# Before (master)
git checkout master
bundle exec rubocop --format offenses $files | grep Lint/RedundantCopDisableDirective
8  Lint/RedundantCopDisableDirective

# After (this MR)
git checkout -
bundle exec rubocop --format offenses $files | grep Lint/RedundantCopDisableDirective
# no offenses

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.