widgets: do not render transient messages

Author: williamstein

src/packages/frontend/jupyter/output-messages/message.tsx

@@ -124,6 +124,9 @@ export const CellOutputMessages: React.FC<CellOutputMessagesProps> = React.memo(
     for (const n of numericallyOrderedKeys(obj)) {
       const mesg = obj[n];
       if (mesg != null) {
+        if (mesg.get("transient")) {
+          continue;
+        }
         if (mesg.get("traceback")) {
           hasError = true;
           traceback += mesg.get("traceback").join("\n") + "\n";