Bump rack from 2.2.3.1 to 2.2.6.4 in /example

Bumps [rack](https://github.com/rack/rack) from 2.2.3.1 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@2.2.3.1...v2.2.6.4)

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

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

example/Gemfile.lock

@@ -172,7 +172,7 @@ GEM
     public_suffix (4.0.7)
     puma (5.6.4)
       nio4r (~> 2.0)
-    rack (2.2.3.1)
+    rack (2.2.6.4)
     rack-test (1.1.0)
       rack (>= 1.0, < 3)
     rainbow (3.1.1)