Add `:requires_admin` tag

So tests can be skipped in environments where admin access is not
available.

qa/qa/specs/features/browser_ui/1_manage/project/add_project_member_spec.rb

 # frozen_string_literal: true
 
 module QA
-  RSpec.describe 'Manage' do
+  RSpec.describe 'Manage', :requires_admin do
     describe 'Add project member' do
       before do
         Runtime::Feature.enable('vue_project_members_list')

qa/qa/specs/features/browser_ui/2_plan/email/trigger_email_notification_spec.rb

 # frozen_string_literal: true
 
 module QA
-  RSpec.describe 'Plan', :orchestrated, :smtp do
+  RSpec.describe 'Plan', :orchestrated, :smtp, :requires_admin do
     describe 'Email Notification' do
       include Support::Api
 

qa/qa/specs/features/ee/browser_ui/1_manage/group/group_audit_logs_1_spec.rb

@@ -100,7 +100,7 @@ module QA
         it_behaves_like 'audit event', ['Added user access as Guest', 'Changed access level', 'Removed user access']
       end
 
-      context 'Add and remove project access', testcase: 'https://gitlab.com/gitlab-org/quality/testcases/-/issues/735' do
+      context 'Add and remove project access', :requires_admin, testcase: 'https://gitlab.com/gitlab-org/quality/testcases/-/issues/735' do
         before do
           Runtime::Feature.enable('vue_project_members_list', project: project)