fix: Item tax template not getting mapped from source to traget doc (#21862)

diff --git a/erpnext/public/js/controllers/transaction.js b/erpnext/public/js/controllers/transaction.js
index 28c2102..637d3b3 100644
--- a/erpnext/public/js/controllers/transaction.js
+++ b/erpnext/public/js/controllers/transaction.js
@@ -1652,8 +1652,10 @@
 					if(!r.exc) {
 						$.each(me.frm.doc.items || [], function(i, item) {
 							if(item.item_code && r.message.hasOwnProperty(item.item_code)) {
-								item.item_tax_template = r.message[item.item_code].item_tax_template;
-								item.item_tax_rate = r.message[item.item_code].item_tax_rate;
+								if (!item.item_tax_template) {
+									item.item_tax_template = r.message[item.item_code].item_tax_template;
+									item.item_tax_rate = r.message[item.item_code].item_tax_rate;
+								}
 								me.add_taxes_from_item_tax_template(item.item_tax_rate);
 							} else {
 								item.item_tax_template = "";