COMP: Docker build suddenly stopped working, needs classic solver

[cookpa]

Something under the hood is causing the mamba solver to fail, reproduced on my Ubuntu machine as well as on the GHA runner. Using the classic solver appears to fix it

[gdevenyi]

This doesn't look the "best practice" for setting up a config:

conda config --add channels defaults
conda config --add channels conda-forge
conda config --set channel_priority strict

[gdevenyi]

Personally, I've had very good results switching to the micromamba docker and building up an environment using it:
https://micromamba-docker.readthedocs.io/

[coveralls]

coverage: 84.688%. remained the same
when pulling 839496b on conda_classic_solver
into c4f0e32 on master.

[cookpa]

Merging for now because it's working again, a rewrite for micromamba would be a good idea later