[FIX] point_of_sale: do not merge refund orderline to ordinary line

Part-of: odoo/odoo#77903

addons/point_of_sale/static/src/js/models.js

@@ -2095,6 +2095,8 @@ exports.Orderline = Backbone.Model.extend({
             return false;
         }else if (orderline.get_customer_note() !== this.get_customer_note()) {
             return false;
+        } else if (this.refunded_orderline_id) {
+            return false;
         }else{
             return true;
         }