fix: improved the conditions for determining voucher subtypes

(cherry picked from commit 00eee16)

erpnext/controllers/accounts_controller.py

@@ -1096,9 +1096,11 @@ def get_voucher_subtype(self):
 			return "Purchase Return"
 		elif self.doctype == "Delivery Note" and self.is_return:
 			return "Sales Return"
-		elif (self.doctype == "Sales Invoice" and self.is_return) or self.doctype == "Purchase Invoice":
+		elif self.doctype == "Sales Invoice" and self.is_return:
 			return "Credit Note"
-		elif (self.doctype == "Purchase Invoice" and self.is_return) or self.doctype == "Sales Invoice":
+		elif self.doctype == "Sales Invoice" and self.is_debit_note:
+			return "Debit Note"
+		elif self.doctype == "Purchase Invoice" and self.is_return:
 			return "Debit Note"
 
 		return self.doctype