fix: include missing payment_gateway parameter in Payment Request URL

(cherry picked from commit dbac8cf)

erpnext/accounts/doctype/payment_request/payment_request.py

@@ -246,6 +246,7 @@ def get_payment_url(self):
 				"payer_name": data.customer_name,
 				"order_id": self.name,
 				"currency": self.currency,
+				"payment_gateway": self.payment_gateway,
 			}
 		)