fix: Discount and taxes in return document should follow the reference document (backport #41911) (#42573)

* fix: Discount and taxes in return document should follow the reference document (#41911)

* fix: Discount and taxes in return document should follow the reference document

* fix: Ignore Pricing rule on debit/credit note if created against PI/SI with test cases

* fix: linter issue

(cherry picked from commit 281198456d)

# Conflicts:
#	erpnext/controllers/sales_and_purchase_return.py

* fix: resolved conflict

---------

Co-authored-by: Nabin Hait <nabinhait@gmail.com>

erpnext/controllers/accounts_controller.py

@@ -84,7 +84,6 @@ force_item_fields = (
 	"brand",
 	"stock_uom",
 	"is_fixed_asset",
-	"item_tax_rate",
 	"pricing_rules",
 	"weight_per_unit",
 	"weight_uom",
@@ -707,7 +706,6 @@ class AccountsController(TransactionBase):
 						args["is_subcontracted"] = self.is_subcontracted
 
 					ret = get_item_details(args, self, for_validate=for_validate, overwrite_warehouse=False)
-
 					for fieldname, value in ret.items():
 						if item.meta.get_field(fieldname) and value is not None:
 							if item.get(fieldname) is None or fieldname in force_item_fields:
@@ -717,7 +715,10 @@ class AccountsController(TransactionBase):
 								fieldname
 							):
 								item.set(fieldname, value)
-
+							elif fieldname == "item_tax_rate" and not (
+								self.get("is_return") and self.get("return_against")
+							):
+								item.set(fieldname, value)
 							elif fieldname == "serial_no":
 								# Ensure that serial numbers are matched against Stock UOM
 								item_conversion_factor = item.get("conversion_factor") or 1.0