Fix refund notification registration

Author: schurter-cw

app/code/Magento/Sales/Model/Order/Payment.php

@@ -747,7 +747,7 @@ public function registerRefundNotification($amount)
             true
         )->setAutomaticallyCreated(
             true
-        )->register()->addComment(
+        )->addComment(
             __('The credit memo has been created automatically.')
         );
         $creditmemo->save();