[Security] Bump rack from 2.0.7 to 2.0.8 (#12654)

Bumps [rack](https://github.com/rack/rack) from 2.0.7 to 2.0.8. **This update includes a security fix.**
- [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/2.0.7...2.0.8)

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

Gemfile.lock

@@ -458,7 +458,7 @@ GEM
     pundit (2.1.0)
       activesupport (>= 3.0.0)
     raabro (1.1.6)
-    rack (2.0.7)
+    rack (2.0.8)
     rack-attack (6.2.1)
       rack (>= 1.0, < 3)
     rack-cors (1.1.0)