[16.0][FIX] pos_partner_birthdate: fixing this.changes when add birth…

…date_date

use useState

pos_partner_birthdate/static/src/js/ClientDetailsEdit.esm.js

@@ -1,15 +1,16 @@
 /** @odoo-module **/
+const {useState} = owl;
 import PartnerDetailsEdit from "point_of_sale.PartnerDetailsEdit";
 import Registries from "point_of_sale.Registries";
 
 const PartnerDetailsEditBirthdate = (OriginalPartnerDetailsEdit) =>
     class extends OriginalPartnerDetailsEdit {
         setup() {
             super.setup();
-            this.changes = {
+            this.changes = useState({
                 ...this.changes,
                 birthdate_date: this.props.partner.birthdate_date || null,
-            };
+            });
         }
     };