Add index for `user_bans.user_id`

db/migrate/20231209212629_add_index_on_user_bans_user_id.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class AddIndexOnUserBansUserId < ActiveRecord::Migration[7.0]
+  def change
+    add_index :user_bans, :user_id
+  end
+end