After using whl2conda install cannot install other packages using conda with libmamba solver

[analog-cbarber]

Due to a bug in conda, once you install a package into
an environment from a conda file, attempts to install additional packages using the default libmamba solver
will result in an InvalidMatchSpec error, e.g.

$ conda install -n foobar pytest
Channels:
 - defaults
Platform: osx-arm64
Collecting package metadata (repodata.json): done
Solving environment: failed

InvalidMatchSpec: Invalid spec 'tomlkit[url=file:///Users/Christopher.Barber/miniconda3/pkgs/tomlkit-0.12.3-py_0.conda]': Libmamba only supports a subset of the MatchSpec interface for now. You can only use ('name', 'version', 'build', 'channel', 'subdir'), but you tried to use ('url',).

This does not appear to be a problem if you are using mamba or the classic solver. If you are using conda and not mamba,
you can either explicitly request the classic solver using --solver classic or you can make that the default for that environment
by activating the environment and running:

conda config --env --set solver classic

We should probably have whl2conda install do the latter automatically.

[analog-cbarber]

The original conda bug moved to conda/conda-libmamba-solver#418

It looks like it is getting fixed soon...