Simplify trigger email notification test

It's better to have the implementation details encapsulated in a
method that is called by the test than having all of it inside the
test itself. This way the `it` block gets cleaner and more focused.

qa/qa/specs/features/browser_ui/2_plan/email/trigger_email_notification_spec.rb

@@ -22,8 +22,15 @@ module QA
 
         expect(page).to have_content(/@#{user.username}(\n| )?Given access/)
 
-        # Wait for Action Mailer to deliver messages
-        mailhog_json = Support::Retrier.retry_until(sleep_interval: 1) do
+        mailhog_items = mailhog_json.dig('items')
+
+        expect(mailhog_items).to include(an_object_satisfying { |o| /project was granted/ === o.dig('Content', 'Headers', 'Subject', 0) })
+      end
+
+      private
+
+      def mailhog_json
+        Support::Retrier.retry_until(sleep_interval: 1) do
           Runtime::Logger.debug(%Q[retrieving "#{QA::Runtime::MailHog.api_messages_url}"])
 
           mailhog_response = get QA::Runtime::MailHog.api_messages_url
@@ -33,10 +40,6 @@ module QA
           # Expect at least two invitation messages: group and project
           mailhog_data if mailhog_data.dig('total') >= 2
         end
-
-        # Check json result from mailhog
-        mailhog_items = mailhog_json.dig('items')
-        expect(mailhog_items).to include(an_object_satisfying { |o| /project was granted/ === o.dig('Content', 'Headers', 'Subject', 0) })
       end
     end
   end