New release for JupyterLite 0.4.0 support

[jtpio]

JupyterLite 0.4.0 was released a couple of days ago: https://github.com/jupyterlite/jupyterlite/releases/tag/v0.4.0

#193 relaxed the dependency on jupyterlite-core to be able to use the new version, but it has not been released yet.

I think we can release 0.16.3 now to allow using the latest jupyterlite-sphinx and jupyterlite-core together.

cc @steppi @Carreau @martinRenou for awareness

[jtpio]

Closing as fixed by https://github.com/jupyterlite/jupyterlite-sphinx/releases/tag/v0.16.3.

Conda forge PR: conda-forge/jupyterlite-sphinx-feedstock#32