Bump rack from 3.1.18 to 3.1.20 (#34)

Bumps [rack](https://github.com/rack/rack) from 3.1.18 to 3.1.20.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/main/CHANGELOG.md)
- [Commits](rack/rack@v3.1.18...v3.1.20)

---
updated-dependencies:
- dependency-name: rack
  dependency-version: 3.1.20
  dependency-type: indirect
...

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Author: dependabot[bot]

Gemfile.lock

@@ -90,7 +90,7 @@ GEM
       stringio
     public_suffix (6.0.0)
     racc (1.8.1)
-    rack (3.1.18)
+    rack (3.1.20)
     rack-session (2.1.1)
       base64 (>= 0.1.0)
       rack (>= 3.0.0)