fix: recalculate tax withholding during Purchase Order child update

Author: Navin-S-R

erpnext/controllers/accounts_controller.py

@@ -4054,6 +4054,7 @@ def validate_fg_item_for_subcontracting(new_data, is_new):
 
 	parent.set_payment_schedule()
 	if parent_doctype == "Purchase Order":
+		parent.set_tax_withholding()
 		parent.validate_minimum_order_qty()
 		parent.validate_budget()
 		if parent.is_against_so():