Bump rack in /sample-apps/manual-instrumentation/ruby-on-rails (#95)

Bumps [rack](https://github.com/rack/rack) from 2.2.6.2 to 2.2.6.4.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/main/CHANGELOG.md)
- [Commits](rack/rack@v2.2.6.2...v2.2.6.4)

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

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Author: dependabot[bot]

sample-apps/manual-instrumentation/ruby-on-rails/Gemfile.lock

@@ -191,7 +191,7 @@ GEM
     puma (6.0.2)
       nio4r (~> 2.0)
     racc (1.6.2)
-    rack (2.2.6.2)
+    rack (2.2.6.4)
     rack-test (2.0.2)
       rack (>= 1.3)
     rails (7.0.4.2)