chore: bump rack from 2.2.11 to 2.2.13 in /examples/ruby/backend (#9749)

Bumps [rack](https://github.com/rack/rack) from 2.2.11 to 2.2.13.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/main/CHANGELOG.md)
- [Commits](rack/rack@v2.2.11...v2.2.13)

---
updated-dependencies:
- dependency-name: rack
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

examples/ruby/backend/Gemfile.lock

@@ -4,7 +4,7 @@ GEM
     nio4r (2.7.3)
     puma (5.6.9)
       nio4r (~> 2.0)
-    rack (2.2.11)
+    rack (2.2.13)
     rack-unreloader (1.7.0)
 
 PLATFORMS