Bump rack from 2.0.4 to 2.2.6.4 in /2.7/test/rack-test-app

Bumps [rack](https://github.com/rack/rack) from 2.0.4 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@2.0.4...v2.2.6.4)

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

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

2.7/test/rack-test-app/Gemfile.lock

@@ -2,7 +2,7 @@ GEM
  remote: https://rubygems.org/
  specs:
  mustermann (1.0.1)
- rack (2.0.4)
+ rack (2.2.6.4)
  rack-protection (2.0.0)
  rack
  sinatra (2.0.0)