Mambaforge is deprecated

[rickecon]

In many of our repositories, including this one, we use the Mambaforge installer as our small-footprint Python installer in our GitHub Actions. However, Mambaforge is being deprecated and Miniforge is taking its place (see this blog post). Key points are that Mambaforge is going away and Miniforge is taking its place. The sunsetting schedule listed in the link tells us that we will begin to experience more and more incovenient delays in our GH Actions until we make this switch. And Mambaforge will be completely gone by January 2025.

cc: @jdebacker