build(deps): bump rack in /test/preflight/fixtures/example-buildpack

Bumps [rack](https://github.com/rack/rack) from 3.2.1 to 3.2.3.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/main/CHANGELOG.md)
- [Commits](rack/rack@v3.2.1...v3.2.3)

---
updated-dependencies:
- dependency-name: rack
  dependency-version: 3.2.3
  dependency-type: direct:production
...

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

Author: dependabot[bot]

test/preflight/fixtures/example-buildpack/Gemfile.lock

@@ -8,7 +8,7 @@ GEM
     nio4r (2.7.4)
     puma (6.5.0)
       nio4r (~> 2.0)
-    rack (3.2.1)
+    rack (3.2.3)
     rack-protection (4.1.1)
       base64 (>= 0.1.0)
       logger (>= 1.6.0)