Mamba support is experimental

[ccbaumler]

Under the workflows in Github>Actions>Dev Env Instructions the warning shown below may be found:

mamba
Mamba support is still experimental and can result in differently solved environments!

Is this at all a concern? Would it be best to specify the version of Mamba to use in the yml instead of the latest?

@ctb states:

I actually don't find any references anywhere to a dev_env.yml - where are you seeing this? :)

In any case, if it's not related to either the functionality being implemented for the PR, or the changed files, then it's not relevant to the PR & you should start a new issue with that as a question, I think!

[ctb]

(see review comments here, #2106)

[luizirber]

This is a message from setup-miniconda, documented here:
https://github.com/conda-incubator/setup-miniconda#example-6-mamba

@ctb error here: https://github.com/sourmash-bio/sourmash/runs/7239595293?check_suite_focus=true#step:4:590