chore: Bump rack from 3.0.8 to 3.0.9 (#797)

Bumps [rack](https://github.com/rack/rack) from 3.0.8 to 3.0.9.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/main/CHANGELOG.md)
- [Commits](https://github.com/rack/rack/compare/v3.0.8...v3.0.9)

---
updated-dependencies:
- dependency-name: rack
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Gemfile

@@ -33,7 +33,7 @@ gem 'kramdown'
 gem 'liquid'
 gem 'listen'
 gem 'mercenary'
-gem 'rack', '~> 3.0.8'
+gem 'rack', '~> 3.0.9'
 gem 'railties', '>= 5.2.2.1'
 gem 'rouge'
 gem 'rubocop'