Bump rubocop-ast from 0.3.0 to 0.4.0 (#14785)

Bump rubocop-ast from 0.3.0 to 0.4.0 (#14785)

Bumps [rubocop-ast](https://github.com/rubocop-hq/rubocop-ast) from 0.3.0 to 0.4.0.
- [Release notes](https://github.com/rubocop-hq/rubocop-ast/releases)
- [Changelog](https://github.com/rubocop-hq/rubocop-ast/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rubocop-hq/rubocop-ast/compare/v0.3.0...v0.4.0)

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