Fix and simplify check xss occurence in @mentions spec

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

@@ -2,14 +2,15 @@
 
 module QA
   RSpec.describe 'Plan', :reliable do
-    let(:user) do
+    let!(:user) do
       Resource::User.fabricate_via_api! do |user|
         user.name = "eve <img src=x onerror=alert(2)&lt;img src=x onerror=alert(1)&gt;"
         user.password = "test1234"
+        user.api_client = Runtime::API::Client.as_admin
       end
     end
 
-    let(:project) do
+    let!(:project) do
       Resource::Project.fabricate_via_api! do |project|
         project.name = 'xss-test-for-mentions-project'
       end
@@ -17,16 +18,6 @@ module QA
 
     describe 'check xss occurence in @mentions in issues', :requires_admin do
       before do
-        QA::Runtime::Env.personal_access_token = QA::Runtime::Env.admin_personal_access_token
-
-        unless QA::Runtime::Env.personal_access_token
-          Flow::Login.sign_in_as_admin
-        end
-
-        QA::Runtime::Env.personal_access_token = nil
-
-        Page::Main::Menu.perform(&:sign_out) if Page::Main::Menu.perform { |p| p.has_personal_area?(wait: 0) }
-
         Flow::Login.sign_in
 
         Flow::Project.add_member(project: project, username: user.username)