Fix broken tests for older Rails versions

doorkeeper-gem#1736 broke tests for
Rails < 7.1 because these versions compared
`config.action_dispatch.show_exceptions == false`. Conditionally set
this value in the test set up to fix the broken tests.

Author: stanhu

spec/dummy/config/environments/test.rb

@@ -23,7 +23,10 @@
   config.action_controller.perform_caching = false
 
   # Raise exceptions instead of rendering exception templates
-  config.action_dispatch.show_exceptions = :none
+  # Rails 7.1 deprecated false in favor of :none, but we need to use false for
+  # backwards compatibility: https://github.com/rails/rails/pull/45867
+  config.action_dispatch.show_exceptions =
+    Gem::Version.new(Rails.version) >= Gem::Version.new('7.1.0') ? :none : false
 
   # Disable request forgery protection in test environment
   config.action_controller.allow_forgery_protection = false