Fix file locking spec and quarantine sub test

Test was quarantined due to a bug: https://gitlab.com/gitlab-org/gitlab/issues/35254
Changed hardcoded "Adminstrator" in expectation to a username

qa/qa/specs/features/ee/browser_ui/3_create/repository/file_locking_spec.rb

@@ -29,7 +29,8 @@ module QA
         end
       end
 
-      it 'locks a directory and tries to push as a second user' do
+      # Bug issue: https://gitlab.com/gitlab-org/gitlab/issues/35254
+      it 'locks a directory and tries to push as a second user', :quarantine do
         push branch: 'master', file: 'directory/file', as_user: @user_one
 
         sign_out_and_sign_in_as user: @user_one
@@ -74,7 +75,7 @@ module QA
         click_lock
         sign_out_and_sign_in_as user: @user_one
         try_to_merge merge_request: merge_request
-        expect(page).to have_text("locked by Administrator")
+        expect(page).to have_text("locked by #{admin_username}")
       end
 
       it 'locks a file and unlocks in list' do
@@ -150,6 +151,12 @@ module QA
       def expect_no_error_on_push(for_file: 'file', as_user:)
         expect { push branch: 'master', file: for_file, as_user: as_user }.not_to raise_error
       end
+
+      def admin_username
+        Resource::User.fabricate_via_api! do |user|
+          user.username = Runtime::User.username
+        end.name
+      end
     end
   end
 end