Upgrade minitest gem version to 6.0

Author: thompson-tomo

instrumentation/rails/Gemfile

@@ -10,7 +10,7 @@ gemspec
 
 group :test do
   gem 'appraisal', '~> 2.5'
-  gem 'minitest', '~> 5.0'
+  gem 'minitest', '~> 6.0'
   gem 'opentelemetry-sdk', '~> 1.1'
   gem 'opentelemetry-test-helpers', '~> 0.3'
   gem 'rack-test', '~> 2.2.0'