Enable RSpec zero monkey patching mode

The plan for RSpec 4.0 is to disable monkey patching.

See https://github.com/rspec/rspec-core/blob/main/features/configuration/zero_monkey_patching_mode.feature for details.

spec/controllers/sys_controller_spec.rb

@@ -28,7 +28,7 @@
 
 require 'spec_helper'
 
-describe SysController, with_settings: { sys_api_enabled: true } do
+RSpec.describe SysController, with_settings: { sys_api_enabled: true } do
   let(:commit_role) do
     create(:role, permissions: %i[commit_access browse_repository])
   end