Change CI to use miniconda

[johnjasa]

We expect our users to install HOPP through a conda env. We should test our code in CI using a conda env also. This would allow for easier debugging, such as providing a way to reliably reproduce CI environments locally by outputting a conda env file.

This came up because I wanted to output a conda env while debugging on CI, but because we're just using the system Python that wasn't immediately helpful. Here's the commit where I did that and that capability should be added as part of resolving this issue.