Merge branch '#22609' into 'master'

Moves `spec/mailers/shared/notify.rb` to `spec/support/notify_shared_examples.rb`

Closes #22609 

See merge request !6605

spec/mailers/emails/builds_spec.rb

 require 'spec_helper'
 require 'email_spec'
-require 'mailers/shared/notify'
 
 describe Notify do
   include EmailSpec::Matchers

spec/mailers/emails/merge_requests_spec.rb

 require 'spec_helper'
 require 'email_spec'
-require 'mailers/shared/notify'
 
 describe Notify, "merge request notifications" do
   include EmailSpec::Matchers

spec/mailers/emails/profile_spec.rb

 require 'spec_helper'
 require 'email_spec'
-require 'mailers/shared/notify'
 
 describe Notify do
   include EmailSpec::Matchers

spec/mailers/notify_spec.rb

 require 'spec_helper'
 require 'email_spec'
-require 'mailers/shared/notify'
 
 describe Notify do
   include EmailSpec::Helpers