Fix kernel WebSocket protocol

[davidbrochart]

Fixes #1103
Fixes jupyterlab/jupyterlab#13481

[codecov]

Codecov Report

Base: 80.03% // Head: 39.33% // Decreases project coverage by -40.70% ⚠️

Coverage data is based on head (72c848c) compared to base (c2275a7).
Patch coverage: 33.33% of modified lines in pull request are covered.

❗ Current head 72c848c differs from pull request most recent head c0f3f3c. Consider uploading reports for the commit c0f3f3c to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1110       +/-   ##
===========================================
- Coverage   80.03%   39.33%   -40.71%     
===========================================
  Files          68       68               
  Lines        8011     8013        +2     
  Branches     1586     1586               
===========================================
- Hits         6412     3152     -3260     
- Misses       1178     4665     +3487     
+ Partials      421      196      -225     

Impacted Files	Coverage Δ
jupyter_server/services/kernels/websocket.py	38.00% <12.50%> (-45.34%)	⬇️
...ter_server/services/kernels/connection/channels.py	16.11% <75.00%> (-43.37%)	⬇️
...pyter_server/services/contents/largefilemanager.py	11.11% <0.00%> (-72.73%)	⬇️
jupyter_server/services/contents/fileio.py	22.10% <0.00%> (-67.90%)	⬇️
...upyter_server/services/contents/filecheckpoints.py	22.35% <0.00%> (-67.65%)	⬇️
jupyter_server/gateway/handlers.py	0.00% <0.00%> (-61.82%)	⬇️
jupyter_server/services/sessions/sessionmanager.py	27.18% <0.00%> (-61.30%)	⬇️
jupyter_server/auth/utils.py	33.33% <0.00%> (-60.61%)	⬇️
jupyter_server/services/contents/filemanager.py	13.98% <0.00%> (-60.59%)	⬇️
jupyter_server/services/contents/manager.py	27.33% <0.00%> (-59.00%)	⬇️
... and 41 more

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[Zsailer]

You're the man, David! 🚀 Thank you for working on this. I'll give this a review later today.

[blink1073]

LGTM, thanks @davidbrochart!