CTRL+SHIFT+Q shortcut for "Close and Shut Down Notebook" does not work

[JasonWeill]

On macOS Ventura 13.6.6 (22G630), with Firefox and Chrome, CTRL+SHIFT+Q appears in the File menu as a shortcut for "Close and Shut Down Notebook", but pressing this shortcut does not appear to do anything.

On Windows 10, with Firefox, pressing CTRL+SHIFT+Q immediately closes the browser and does not shut down notebook.

Originally reported by @jph00 in #7041.

[JasonWeill]

This code is present in JupyterLab, on which Notebook is based, and this bug is also present in JupyterLab. Closing in favor of jupyterlab/jupyterlab#16330.