[Fix #8165] Require Parser gem 2.7.1.5

[koic]

Fixes #8165 and Follows whitequark/parser#729.

Parser 2.7.1.5 includes whitequark/parser#717 and fixes #8165. And this PR updates Ruby 2.8 to Ruby 3.0.

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• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
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• Squashed related commits together.
• Added tests.
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[koic]

This PR should be synchronized with rubocop/rubocop-ast#121 for the successful build.