Fix `Rails/WhereExists` cop in FeaturedTag model (#28791)

.rubocop_todo.yml

@@ -82,7 +82,6 @@ Rails/WhereExists:
     - 'app/lib/feed_manager.rb'
     - 'app/lib/status_cache_hydrator.rb'
     - 'app/lib/suspicious_sign_in_detector.rb'
-    - 'app/models/featured_tag.rb'
     - 'app/models/poll.rb'
     - 'app/models/session_activation.rb'
     - 'app/models/status.rb'

app/models/featured_tag.rb

@@ -66,6 +66,10 @@ class FeaturedTag < ApplicationRecord
   end
 
   def validate_tag_uniqueness
-    errors.add(:name, :taken) if FeaturedTag.by_name(name).where(account_id: account_id).exists?
+    errors.add(:name, :taken) if tag_already_featured_for_account?
+  end
+
+  def tag_already_featured_for_account?
+    FeaturedTag.by_name(name).exists?(account_id: account_id)
   end
 end