fix: don't make naming series mandatory for items

Item variants are an exception, hence this needs to be checked
conditionally.
diff --git a/erpnext/setup/doctype/naming_series/naming_series.py b/erpnext/setup/doctype/naming_series/naming_series.py
index 4def6eb..986b4e8 100644
--- a/erpnext/setup/doctype/naming_series/naming_series.py
+++ b/erpnext/setup/doctype/naming_series/naming_series.py
@@ -180,11 +180,11 @@
 		prefix = parse_naming_series(parts)
 		return prefix
 
-def set_by_naming_series(doctype, fieldname, naming_series, hide_name_field=True):
+def set_by_naming_series(doctype, fieldname, naming_series, hide_name_field=True, make_mandatory=1):
 	from frappe.custom.doctype.property_setter.property_setter import make_property_setter
 	if naming_series:
 		make_property_setter(doctype, "naming_series", "hidden", 0, "Check", validate_fields_for_doctype=False)
-		make_property_setter(doctype, "naming_series", "reqd", 1, "Check", validate_fields_for_doctype=False)
+		make_property_setter(doctype, "naming_series", "reqd", make_mandatory, "Check", validate_fields_for_doctype=False)
 
 		# set values for mandatory
 		try:
diff --git a/erpnext/stock/doctype/stock_settings/stock_settings.py b/erpnext/stock/doctype/stock_settings/stock_settings.py
index 2dd103d..1de48b6 100644
--- a/erpnext/stock/doctype/stock_settings/stock_settings.py
+++ b/erpnext/stock/doctype/stock_settings/stock_settings.py
@@ -20,7 +20,7 @@
 
 		from erpnext.setup.doctype.naming_series.naming_series import set_by_naming_series
 		set_by_naming_series("Item", "item_code",
-			self.get("item_naming_by")=="Naming Series", hide_name_field=True)
+			self.get("item_naming_by")=="Naming Series", hide_name_field=True, make_mandatory=0)
 
 		stock_frozen_limit = 356
 		submitted_stock_frozen = self.stock_frozen_upto_days or 0