Avoid `macos-latest` Python version compatibility issues in GitHub Actions runner images

[d33bs]

Description

This PR addresses #195, enabling MacOS testing to take place. Based on a recent successful job run, I believe this is a major version jump from macos-12 to macos-13 in an effort to keep the declarative nature of this "more protected" from deprecations as they occur (for the time being).

If all looks good here, I plan to create an issue which helps us remember to update the MacOS version specification to a more compatible version when able or desired.

Closes #195 Required for #194 and other PR's in order to resolve GH Actions failures.

What is the nature of your change?

• [x] Bug fix (fixes an issue).
• [ ] Enhancement (adds functionality).
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected).
• [ ] This change requires a documentation update.

Checklist

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• [x] I have performed a self-review of my own code.
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• [ ] I have made corresponding changes to the documentation.
• [x] My changes generate no new warnings.
• [x] New and existing unit tests pass locally with my changes.
• [ ] I have added tests that prove my fix is effective or that my feature works.
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[d33bs]

Thank you @gwaybio ! Merging this in.