[micromamba] 0.21.0 breaks PIP_ config env variables

[austin1howard]

In Mamba micromamba 0.21.0, environment variables starting with PIP_ (used to configure pip for things like extra indexes, etc.) are being stripped. I think this is part of #1422, in particular this change: wolfv@61c5de7#diff-ebac1cb6982f8e508ff9d8203d56f74aa3da80115d7ca84cc525a131ef23535aR61

There may be good reason to suppress some environment variables, but this line's change only applies to running pip (or in the future some other third party package manager) so I don't think it makes sense to empty the environment variables. At least, env vars which start with PIP_ should be passed through.

[austin1howard]

I suppose this is more directly related to #1413.

[wolfv]

Hi @austin1howard thanks for letting us know. I think it totally makes sense to run the pip command with a pass-through environment so that all env variables are inherited.

[wolfv]

I've tagged this with micromamba because I don't think this concerns mamba. Correct?

[austin1howard]

yeah seems so, I'm able to install through "regular" mamba v0.21.

[austin1howard]

I know it's trivial but I pushed a PR to remove that line.

[wolfv]

Thanks!