Update rack requirement from ~> 2.2 to ~> 3.0

Updates the requirements on [rack](https://github.com/rack/rack) to permit the latest version.
- [Release notes](https://github.com/rack/rack/releases)
- [Changelog](https://github.com/rack/rack/blob/main/CHANGELOG.md)
- [Commits](rack/rack@2.2.0...v3.0.8)

---
updated-dependencies:
- dependency-name: rack
  dependency-type: direct:development
...

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

Gemfile

@@ -10,7 +10,7 @@ group :development, :test do
   gem 'bake-test-external'
   gem 'coveralls_reborn', require: false
   gem 'pry'
-  gem 'rack', '~> 2.2'
+  gem 'rack', '~> 3.0'
   gem 'rake'
   gem 'rspec', '~> 3.7'
   gem 'rspec_junit_formatter', '~> 0.4'