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)

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Gemfile.lock

@@ -544,7 +544,7 @@ GEM
       rubocop-ast (>= 0.3.0, < 1.0)
       ruby-progressbar (~> 1.7)
       unicode-display_width (>= 1.4.0, < 2.0)
-    rubocop-ast (0.3.0)
+    rubocop-ast (0.4.0)
       parser (>= 2.7.1.4)
     rubocop-rails (2.8.0)
       activesupport (>= 4.2.0)