Bump rack from 2.2.8 to 2.2.8.1 in /backend

Bumps [rack](https://github.com/rack/rack) from 2.2.8 to 2.2.8.1.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/main/CHANGELOG.md)
- [Commits](rack/rack@v2.2.8...v2.2.8.1)

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

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

Author: dependabot[bot]

backend/Gemfile.lock

@@ -324,7 +324,7 @@ GEM
     pusher-signature (0.1.8)
     racc (1.7.3)
     racc (1.7.3-java)
-    rack (2.2.8)
+    rack (2.2.8.1)
     rack-cors (2.0.1)
       rack (>= 2.0.0)
     rack-test (2.1.0)