Use around hook to restore context in ApplicationHelper spec (#3432)

spec/helpers/application_helper_spec.rb

@@ -100,6 +100,12 @@ describe ApplicationHelper do
   end
 
   describe 'title' do
+    around do |example|
+      site_title = Setting.site_title
+      example.run
+      Setting.site_title = site_title
+    end
+
     it 'returns site title on production enviroment' do
       Setting.site_title = 'site title'
       expect(Rails.env).to receive(:production?).and_return(true)