Rolled back ipywidgets to ==8.1.1

[rmhowie]

This pull request rolls back the version of ipywidgets to ==8.1.1 as 8.1.2 broke the widget examples when I tested them.

On my cloned version of the demo repo, this change to requirements.txt fixed the issue.

Thanks for your hard work on this terrific project!

[jtpio]

@rmhowie looks like this may be fixed by the new jupyterlite-pyodide-kernel==0.2.3? Which includes this fix: https://github.com/jupyterlite/pyodide-kernel/pull/86

If so maybe we could update jupyterlite-pyodide-kernel to the latest version?

[rmhowie]

I attempted to fix the issue by reverting the ipwidgets pinning change and changing the pyodide version to jupyterlite-pyodide-kernel==0.2.3 but it didn't seem to work immediately. I might have done something wrong though (e.g., not upgrade other necessary dependancies).

[jtpio]

https://github.com/jupyterlite/demo/pull/135 seems to be fixing it when trying the built artifact:

[jtpio]

Closing as fixed by https://github.com/jupyterlite/demo/pull/135