call and stub the correct method name

lib/gitlab/email/handler/ee/service_desk_handler.rb

@@ -50,7 +50,7 @@ module Gitlab
           end
 
           def send_thank_you_email!
-            Notify.thank_you_email(@issue.id)
+            Notify.service_desk_thank_you_email(@issue.id)
           end
 
           def from_address

spec/lib/gitlab/email/handler/service_desk_handler_spec.rb

@@ -22,7 +22,7 @@ describe Gitlab::Email::Handler::EE::ServiceDeskHandler do
     it 'receives the email' do
       setup_attachment
 
-      expect(Notify).to receive(:thank_you_email).with(instance_of(Fixnum))
+      expect(Notify).to receive(:service_desk_thank_you_email).with(instance_of(Fixnum))
 
       expect { receiver.execute }.to change { Issue.count }.by(1)