Update jwt requirement from >= 2.2, < 2.7 to >= 2.2, < 2.9

Updates the requirements on [jwt](https://github.com/jwt/ruby-jwt) to permit the latest version.
- [Release notes](https://github.com/jwt/ruby-jwt/releases)
- [Changelog](https://github.com/jwt/ruby-jwt/blob/main/CHANGELOG.md)
- [Commits](jwt/ruby-jwt@v2.2.0...v2.8.0)

---
updated-dependencies:
- dependency-name: jwt
  dependency-type: direct:production
...

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

rack-cloudflare-jwt.gemspec

@@ -28,7 +28,7 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency 'simplecov',           '>= 0.16.0'
   spec.add_development_dependency 'webmock',             '>= 3.8.0'
 
-  spec.add_runtime_dependency 'jwt', '>= 2.2', '< 2.7'
+  spec.add_runtime_dependency 'jwt', '>= 2.2', '< 2.9'
   spec.add_runtime_dependency 'multi_json'
   spec.add_runtime_dependency 'rack'
   spec.add_runtime_dependency 'rack-jwt', '>= 0.4.0'