Regularly scheduled tests to catch dependency or CI update/deprecation issues

[zachcran]

Is your feature request related to a problem? Please describe.
During the course of #165, the test_release job (see failed job here) was cancelled due to the ubuntu-20.04 runner being decommissioned on April 15, 2025 by GitHub.

Describe the solution you'd like
Breaking changes in dependencies (package, CI, or otherwise) would be caught sooner if we had regularly scheduled test runs, like nightly builds, to catch these issues sooner. This can be accomplished with the schedule trigger on a workflow (link) using cron syntax.

For example, nightly builds at 00:00 UTC (18:00 CST):

on:
  schedule:
    - cron: '0 0 * * *'

or every Monday:

on:
  schedule:
    - cron: '0 0 * * MON'

or, to save on CI minutes a bit more, every 15 days:

on:
  schedule:
    - cron: '0 0 1,16 * *'

Describe alternatives you've considered
I suppose we could manually check regularly for these issues. We could also do nothing and continue catching the issues as PR tests fail.

Additional context
To create the cron strings, I used https://crontab.guru/ and examples they provide at https://crontab.guru/examples.html.