Update rack-test requirement from ~> 0.7.0 to >= 0.7, < 2.2

Updates the requirements on [rack-test](https://github.com/rack/rack-test) to permit the latest version.
- [Release notes](https://github.com/rack/rack-test/releases)
- [Changelog](https://github.com/rack/rack-test/blob/main/History.md)
- [Commits](rack/rack-test@v0.7.0...v2.1.0)

---
updated-dependencies:
- dependency-name: rack-test
  dependency-type: direct:production
...

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

oxidized-web.gemspec

@@ -26,7 +26,7 @@ Gem::Specification.new do |s|
   s.add_runtime_dependency 'sinatra',             '~> 1.4', '>= 1.4.6'
   s.add_runtime_dependency 'sinatra-contrib',     '~> 1.4', '>= 1.4.6'
   s.add_runtime_dependency 'json',                '~> 2.3'
-  s.add_runtime_dependency 'rack-test',           '~> 0.7.0'
+  s.add_runtime_dependency 'rack-test',           '>= 0.7', '< 2.2'
 
   s.add_development_dependency 'bundler',              '~> 2.2'
   s.add_development_dependency 'rails_best_practices', '~> 1.19'