[Security] Bump rack from 2.0.5 to 2.0.6 (#9214)

Bumps [rack](https://github.com/rack/rack) from 2.0.5 to 2.0.6. **This update includes security fixes.**
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rack/rack/compare/2.0.5...2.0.6

)

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