Change set to let_it_be in ee/spec/graphql

Contributes to https://gitlab.com/gitlab-org/gitlab/issues/27922

ee/spec/graphql/resolvers/design_management/design_resolver_spec.rb

@@ -11,11 +11,11 @@ describe Resolvers::DesignManagement::DesignResolver do
   end
 
   describe "#resolve" do
-    set(:issue) { create(:issue) }
-    set(:project) { issue.project }
-    set(:first_version) { create(:design_version) }
-    set(:first_design) { create(:design, issue: issue, versions: [first_version]) }
-    set(:current_user) { create(:user) }
+    let_it_be(:issue) { create(:issue) }
+    let_it_be(:project) { issue.project }
+    let_it_be(:first_version) { create(:design_version) }
+    let_it_be(:first_design) { create(:design, issue: issue, versions: [first_version]) }
+    let_it_be(:current_user) { create(:user) }
 
     before do
       project.add_developer(current_user)

ee/spec/graphql/resolvers/design_management/version_resolver_spec.rb

@@ -11,10 +11,10 @@ describe Resolvers::DesignManagement::VersionResolver do
   end
 
   describe "#resolve" do
-    set(:issue) { create(:issue) }
-    set(:project) { issue.project }
-    set(:first_version) { create(:design_version) }
-    set(:first_design) { create(:design, issue: issue, versions: [first_version]) }
+    let_it_be(:issue) { create(:issue) }
+    let_it_be(:project) { issue.project }
+    let_it_be(:first_version) { create(:design_version) }
+    let_it_be(:first_design) { create(:design, issue: issue, versions: [first_version]) }
     let(:current_user) { create(:user) }
 
     before do

ee/spec/graphql/resolvers/epic_resolver_spec.rb

@@ -5,8 +5,8 @@ require 'spec_helper'
 describe Resolvers::EpicResolver do
   include GraphqlHelpers
 
-  set(:current_user) { create(:user) }
-  set(:user2) { create(:user) }
+  let_it_be(:current_user) { create(:user) }
+  let_it_be(:user2) { create(:user) }
 
   context "with a group" do
     let(:group)   { create(:group) }