Update JupyterLab 4.2.0 and fix test start store

[davidbrochart]

After https://github.com/jupyter-server/pycrdt-websocket/pull/42, main is broken, see here.

[github-actions[bot]]

:point_left: Launch a Binder on branch _davidbrochart/jupytercollaboration/fix-test

[davidbrochart]

Looks like failures are related to JupyterLab 4.2.0. cc @krassowski @fcollonval

[krassowski]

I think two things need to be done:

• currently the packages pin to alpha versions of JupyterLab 4.2.0 - these need to be bumped for the "outdated packages" failing check to go away
• the snapshots will need to be updated to include the updated UI elements from JupyterLab 4.2.0

[davidbrochart]

Thanks @krassowski, I opened #306.

[davidbrochart]

I rebased this PR on #306.

[davidbrochart]

Finally got it working :smile: Do you want to review @krassowski ?