Define type and coder of serialzed attribute since this is required s…

…in rails 7.1

db/migrate/20230919124243_migrate_group_settings_die_mitte.rb

@@ -43,7 +43,7 @@ class LegacyGroupSetting < ActiveRecord::Base
     self.table_name = 'settings'
     belongs_to :target, polymorphic: true
 
-    serialize :value, Hash
+    serialize :value, type: Hash, coder: YAML
   end
 
   private