fixed undo redo keybindings for notebook editor

[jonah-iden]

What it does

this fixes using ctrcmd+z and ctrlcmd+shift+z keybdinings in notebook editor to undo redo notebook edit operations.

How to test

open a notebook add or remove a cell. while a cell editor is focused undo redo should only work for the editor, if no editor is focused undo redo should work for the full notebook

Follow-ups

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[jbicker]

Works fine! Thanks.