Doesn't (always) work with latest micromamba

[martinRenou]

Description

It seems something changed starting with micromamba 2.0.6 that makes the build fail. See #199

[martinRenou]

This results in having to pin micromamba in the conda package https://github.com/conda-forge/jupyterlite-xeus-feedstock/blob/main/recipe/meta.yaml#L34