Pinning conda-libmamba-solver to only current conda releases

[costrouc]

There are two changes in conda that cause breaking changes in conda-libmamba-solver:

• https://github.com/conda/conda-libmamba-solver/issues/153
• https://github.com/conda/conda-libmamba-solver/issues/152

There is a matching PR for this in conda-forge https://github.com/conda-forge/conda-forge-repodata-patches-feedstock/pull/419

[costrouc]

For review @jaimergp and @jezdez