Bump rack from 3.1.20 to 3.1.21 in the bundler group across 1 directory

Bumps the bundler group with 1 update in the / directory: [rack](https://github.com/rack/rack).


Updates `rack` from 3.1.20 to 3.1.21
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/main/CHANGELOG.md)
- [Commits](rack/rack@v3.1.20...v3.1.21)

---
updated-dependencies:
- dependency-name: rack
  dependency-version: 3.1.21
  dependency-type: indirect
  dependency-group: bundler
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

Gemfile.lock

@@ -75,7 +75,7 @@ GEM
       stringio
     public_suffix (5.0.5)
     racc (1.8.0)
-    rack (3.1.20)
+    rack (3.1.21)
     rainbow (3.1.1)
     rake (13.2.1)
     rdoc (6.7.0)