Using +NEW freezes Jupyterlab completely

**Describe the issue**:
After pressing +NEW button to start a cluster:

* The launching never finishes, seemingly stalls.
* I cannot CTRL-C the Jupyter lab server in the terminal any more.
* I cannot open existing notebooks anymore.
* I do not get any log related to having tried to launch a dask cluster in the terminal.
* I still can get out of the tmux (the detach hotkey still works, so that i can kill the session that way.

As usual, this "WORKED BEFORE" (TM) on this machine, but I hadn't used it for several weeks. :(

**Minimal Complete Verifiable Example**:

* create a new env with python 3.11
* mamba install jupyterlab dask_labextension
* run `jupyter lab .` in a folder with work projects (sub folders with notebooks in them)

**Anything else we need to know?**:

I saw that a new py311 env automatically gets bokeh > 3, so I mamba-installed bokeh<3 to make dashboards work.

**Environment**:

- Dask version: 2023.1.0 (labextension 6.0.0)
- Python version: 3.11
- Operating System: Linux CentOS 7.5.1804 (core)
- Install method (conda, pip, source): conda