[Fix #8864] Fix false positive for Style/RedundantBegin with a postfix while or until

[dvandersluis]

Fixes #8864.

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Before submitting the PR make sure the following are checked:

• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Added an entry to the Changelog if the new code introduces user-observable changes. See changelog entry format.
• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Run bundle exec rake default. It executes all tests and RuboCop for itself, and generates the documentation.

[koic]

This looks good to me. Can you rebase with the latest master branch?

[dvandersluis]

@koic done!

[koic]

Thanks!