Replace set with let_it_be in spec/mailers

Removes usage of `set` in specs

spec/mailers/emails/pages_domains_spec.rb

@@ -7,8 +7,8 @@ describe Emails::PagesDomains do
   include EmailSpec::Matchers
   include_context 'gitlab email notification'
 
-  set(:domain) { create(:pages_domain, project: project) }
-  set(:user) { project.creator }
+  let_it_be(:domain, reload: true) { create(:pages_domain, project: project) }
+  let_it_be(:user) { project.creator }
 
   shared_examples 'a pages domain email' do
     let(:recipient) { user }

spec/mailers/emails/pipelines_spec.rb

@@ -6,7 +6,7 @@ require 'email_spec'
 describe Emails::Pipelines do
   include EmailSpec::Matchers
 
-  set(:project) { create(:project, :repository) }
+  let_it_be(:project) { create(:project, :repository) }
 
   shared_examples_for 'correct pipeline information' do
     it 'has a correct information' do

spec/mailers/notify_spec.rb

@@ -13,11 +13,11 @@ describe Notify do
 
   let(:current_user_sanitized) { 'www_example_com' }
 
-  set(:user) { create(:user) }
-  set(:current_user) { create(:user, email: "current@email.com", name: 'www.example.com') }
-  set(:assignee) { create(:user, email: 'assignee@example.com', name: 'John Doe') }
+  let_it_be(:user) { create(:user) }
+  let_it_be(:current_user) { create(:user, email: "current@email.com", name: 'www.example.com') }
+  let_it_be(:assignee) { create(:user, email: 'assignee@example.com', name: 'John Doe') }
 
-  set(:merge_request) do
+  let_it_be(:merge_request) do
     create(:merge_request, source_project: project,
                            target_project: project,
                            author: current_user,
@@ -25,7 +25,7 @@ describe Notify do
                            description: 'Awesome description')
   end
 
-  set(:issue) do
+  let_it_be(:issue, reload: true) do
     create(:issue, author: current_user,
                    assignees: [assignee],
                    project: project,
@@ -487,7 +487,7 @@ describe Notify do
       end
 
       describe 'that are unmergeable' do
-        set(:merge_request) do
+        let_it_be(:merge_request) do
           create(:merge_request, :conflict,
                  source_project: project,
                  target_project: project,
@@ -568,7 +568,7 @@ describe Notify do
     end
 
     describe '#mail_thread' do
-      set(:mail_thread_note) { create(:note) }
+      let_it_be(:mail_thread_note) { create(:note) }
 
       let(:headers) do
         {
@@ -638,9 +638,9 @@ describe Notify do
       let(:host) { Gitlab.config.gitlab.host }
 
       context 'in discussion' do
-        set(:first_note) { create(:discussion_note_on_issue, project: project) }
-        set(:second_note) { create(:discussion_note_on_issue, in_reply_to: first_note, project: project) }
-        set(:third_note) { create(:discussion_note_on_issue, in_reply_to: second_note, project: project) }
+        let_it_be(:first_note) { create(:discussion_note_on_issue, project: project) }
+        let_it_be(:second_note) { create(:discussion_note_on_issue, in_reply_to: first_note, project: project) }
+        let_it_be(:third_note) { create(:discussion_note_on_issue, in_reply_to: second_note, project: project) }
 
         subject { described_class.note_issue_email(recipient.id, third_note.id) }
 
@@ -664,7 +664,7 @@ describe Notify do
       end
 
       context 'individual issue comments' do
-        set(:note) { create(:note_on_issue, project: project) }
+        let_it_be(:note) { create(:note_on_issue, project: project) }
 
         subject { described_class.note_issue_email(recipient.id, note.id) }