DEV: Bump rack from 2.0.8 to 2.1.1 (#8702)

Bumps [rack](https://github.com/rack/rack) from 2.0.8 to 2.1.1.
- [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/2.0.8...2.1.1)

On a cursory look none of the changes should impact Discourse, we want to be on latest rack so we can benefit from all the latest bug fixes.

Gemfile.lock

@@ -271,7 +271,7 @@ GEM
     puma (4.3.1)
       nio4r (~> 2.0)
     r2 (0.2.7)
-    rack (2.0.8)
+    rack (2.1.1)
     rack-mini-profiler (1.1.4)
       rack (>= 1.2.0)
     rack-openid (1.3.1)