jupyterlab-lsp: pyls acceptance test failing on Ubuntu with Python 3.6 on master

This was not an issue at the release time, but I noticed this on #459 and then re-triggered master to see if this is related to the PR or not (its not):

• Failure (re-triggerred): https://github.com/krassowski/jupyterlab-lsp/runs/1668978098
• Non-failure: https://github.com/krassowski/jupyterlab-lsp/runs/1657936485

All robot tests (except for Smoke and non-pyls tests) fail with:

Setup failed:
Element 'css:div.lsp-statusbar-item' did not get text 'Fully initialized' in 1 minute.

Also teardown failed:
Phrases found in /home/runner/work/jupyterlab-lsp/jupyterlab-lsp/atest/output/linux_36_4/lab.log: {'pyls_jsonrpc.endpoint - Failed to handle request': True}

All other versions seem ok.

Failing now:

python-language-server                         0.36.2  pyhd8ed1ab_0         conda-forge/noarch       Cached
python-jsonrpc-server                           0.4.0  pyh9f0ad1d_0         conda-forge/noarch       Cached

Non-failing (before):

python-language-server                         0.36.2  pyhd8ed1ab_0         conda-forge/noarch       Cached
python-jsonrpc-server                           0.4.0  pyh9f0ad1d_0         conda-forge/noarch       Cached