fix: add non-stock item filter for fg_item in PO

(cherry picked from commit f95ed7d)

erpnext/buying/doctype/purchase_order/purchase_order.js

@@ -33,6 +33,7 @@ frappe.ui.form.on("Purchase Order", {
 		frm.set_query("fg_item", "items", function() {
 			return {
 				filters: {
+					'is_stock_item': 1,
 					'is_sub_contracted_item': 1,
 					'default_bom': ['!=', '']
 				}