Use let syntax

qa/qa/specs/features/browser_ui/2_plan/issue/mentions_spec.rb

@@ -3,17 +3,18 @@
 module QA
   RSpec.describe 'Plan', :smoke, :reliable do
     describe 'mention' do
-      before do
-        Flow::Login.sign_in
-
-        @user = Resource::User.fabricate_or_use(Runtime::Env.gitlab_qa_username_1, Runtime::Env.gitlab_qa_password_1)
-
-        project = Resource::Project.fabricate_via_api! do |project|
+      let(:user) { Resource::User.fabricate_or_use(Runtime::Env.gitlab_qa_username_1, Runtime::Env.gitlab_qa_password_1) }
+      let(:project) do
+        Resource::Project.fabricate_via_api! do |project|
           project.name = 'project-to-test-mention'
           project.visibility = 'private'
         end
+      end
+
+      before do
+        Flow::Login.sign_in
 
-        project.add_member(@user)
+        project.add_member(user)
 
         Resource::Issue.fabricate_via_api! do |issue|
           issue.project = project
@@ -22,7 +23,7 @@ module QA
 
       it 'mentions another user in an issue' do
         Page::Project::Issue::Show.perform do |show|
-          at_username = "@#{@user.username}"
+          at_username = "@#{user.username}"
 
           show.select_all_activities_filter
           show.comment(at_username)