Issue with porting ipkernel_qtapp to PySide6, event loop doesn't quit

Hello,

I was successfully using in process embedded QtConsole example in [my app](https://github.com/SciQLop/SciQLop/blob/main/SciQLop/widgets/console.py).
Now, I want to allow jupyter notebooks to connect to my app kernel, so I switched to IPKernelApp like in [this example](https://github.com/ipython/ipykernel/blob/main/examples/embedding/ipkernel_qtapp.py) but I can't close anymore My app.
The trick that work is to call quit() from the kernel with `self.ipkernel.shell.run_cell("quit()")` or from a QtConsole, using qapp.quit() doesn't seems to work anymore.
Here is a patch if someone want to reproduce the issue with ipykernel example:
[ipykernel_pyside6.zip](https://github.com/ipython/ipykernel/files/13635546/ipykernel_pyside6.zip)