fix: attribute type issue

Author: HassanAkbar

lib/genericode/value.rb

@@ -9,7 +9,7 @@
 
 module Genericode
   class Value < Lutaml::Model::Serializable
-    attribute :column_ref, ColumnRef
+    attribute :column_ref, :string
     attribute :annotation, Annotation
     attribute :simple_value, SimpleValue
     attribute :complex_value, AnyOtherContent