fix: invalid exchange loss booking on invoice againts base accounts

(cherry picked from commit 3d5dba6976)

erpnext/accounts/doctype/payment_entry/payment_entry.py

@@ -350,7 +350,9 @@ class PaymentEntry(AccountsController):
 				ref_details = get_reference_details(
 					d.reference_doctype, d.reference_name, self.party_account_currency
 				)
-				if ref_exchange_rate:
+
+				# Only update exchange rate when the reference is Journal Entry
+				if ref_exchange_rate and d.reference_doctype == "Journal Entry":
 					ref_details.update({"exchange_rate": ref_exchange_rate})
 
 				for field, value in ref_details.items():