BUG/TST: Fix external RC tests, add mac testing, bump NEP29 numpy

[jklenzing]

Description

Updates tests for external optional installs, partially in support of aburrell/aacgmv2#93.

• Fixes a bug where the pre-release candidates are not downloaded
• Adds support for mac tests for the external RC workflow
• Bumps minimum numpy to 1.25 for NEP29 tests

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

via manual workflow initiated here and verifying that

• aacgmv2 2.7.0rc1 is installed
• the optional test test_methods_magcoord.py::TestBasics::test_add_coordinates[add_aacgm_coordinates-targets0] is run and passed

Test Configuration

• Operating system: Mac, ubuntu, windows
• Version number: Python 3.12

Checklist:

• Make sure you are merging into the develop (not main) branch
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• Add a note to CHANGELOG.md, summarizing the changes
• Update zenodo.json file for new code contributors

If this is a release PR, replace the first item of the above checklist with the
release checklist on the pysat wiki:
https://github.com/pysat/pysat/wiki/Checklist-for-Release

[aburrell]

Smart workflow!