fix: convert asynchronous field update to synchronous (#28930)

(cherry picked from commit 5adf85f5b7ba94591381b03709b1fee6aa9331a5)

Co-authored-by: Dan Navarro on Ubuntu Work <danjeremynavarro@gmail.com>

erpnext/public/js/utils.js

@@ -430,12 +430,9 @@ erpnext.utils.select_alternate_items = function(opts) {
 					qty = row.qty;
 				}
 				row[item_field] = d.alternate_item;
-				frm.script_manager.trigger(item_field, row.doctype, row.name)
-					.then(() => {
 				frappe.model.set_value(row.doctype, row.name, 'qty', qty);
-						frappe.model.set_value(row.doctype, row.name,
-							opts.original_item_field, d.item_code);
-					});
+				frappe.model.set_value(row.doctype, row.name, opts.original_item_field, d.item_code);
+				frm.trigger(item_field, row.doctype, row.name);
 			});
 
 			refresh_field(opts.child_docname);