Bump rack from 2.2.17 to 2.2.18 in /benchmarks/shipit (#410)

Bumps [rack](https://github.com/rack/rack) from 2.2.17 to 2.2.18.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/main/CHANGELOG.md)
- [Commits](rack/rack@v2.2.17...v2.2.18)

---
updated-dependencies:
- dependency-name: rack
  dependency-version: 2.2.18
  dependency-type: indirect
...

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

Author: dependabot[bot]

benchmarks/shipit/Gemfile.lock

@@ -228,7 +228,7 @@ GEM
     puma (6.6.1)
       nio4r (~> 2.0)
     racc (1.8.1)
-    rack (2.2.17)
+    rack (2.2.18)
     rack-session (1.0.2)
       rack (< 3)
     rack-test (2.2.0)