Update to the newer module for the devise test helpers

Devise 4.2.0 deprecated the Devise::TestHelpers module in favour of the
Devise::Test::ControllerHelpers module, which is because they wanted to
split the different test helpers into different modules.

https://github.com/heartcombo/devise/blob/main/CHANGELOG.md#420---2016-07-01

spec/spec_helper.rb

@@ -54,7 +54,7 @@
     FixturesSpecHelper.destroy
   end
 
-  config.include Devise::TestHelpers, :type => :controller
+  config.include Devise::Test::ControllerHelpers, :type => :controller
   config.include FixturesSpecHelper, :type => :controller # supply fixtures variables
   config.include ControllersSpecHelper, :type => :controller # some macros for testing controllers
   config.render_views # don't stub views when testing controllers