Cleanup of `main_build.py`

[kenodegard]

Description

A noop PR, just cleaning up formatting and using appropriate helper functions.

Checklist - did you ...

• [x] ~Add a file to the news directory (using the template) for the next release's release notes?~
• [x] ~Add / update necessary tests?~
• [x] ~Add / update outdated documentation?~

[dholth]

When will we run black on the entire conda source code, commit that, and mark it as a revision to ignore for blame purposes?

[kenodegard]

Probably not for another year or so. Looking at the changes here now I'm not sure there's value in doing the string reformatting as I did. Too much noise.

[jezdez]

pre-commit.ci autofix