CI fix: Mambaforge is deprecated and mamba in now the default installer

[bhazelton]

Description

Fixes deprecation warnings on GitHub actions runs about mambaforge going away. Mambaforge and Miniforge are now identical and mamba is the used by default in conda. See https://conda-forge.org/news/2024/07/29/sunsetting-mambaforge/

Motivation and Context

Fixes #1477

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation change (documentation changes only)
• Version change
• Build or continuous integration change

Checklist:

• I have read the contribution guide.
• My code follows the code style of this project.

Build or continuous integration change checklist:

• If required or optional dependencies have changed (including version numbers), I have updated the readme to reflect this.
• If this is a new CI setup, I have added the associated badge to the readme and to references/make_index.py (if appropriate).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.92%. Comparing base (c80821e) to head (15b7e55).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1478   +/-   ##
=======================================
  Coverage   99.92%   99.92%           
=======================================
  Files          61       61           
  Lines       21337    21337           
=======================================
  Hits        21322    21322           
  Misses         15       15           

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[mkolopanis]

looks pretty good to me, should we mark this to close #1477 as well?

[bhazelton]

looks pretty good to me, should we mark this to close #1477 as well?

Ha! I hadn't seen that issue. I'll mark this to close it.