Bump rack-attack from 6.1.0 to 6.2.1 (#12421)

Bumps [rack-attack](https://github.com/kickstarter/rack-attack) from 6.1.0 to 6.2.1.
- [Release notes](https://github.com/kickstarter/rack-attack/releases)
- [Changelog](https://github.com/kickstarter/rack-attack/blob/master/CHANGELOG.md)
- [Commits](https://github.com/kickstarter/rack-attack/compare/v6.1.0...v6.2.1

)

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