CI improvement: add lowest-direct dependency resolution

[rkingsbury]

We should modify the GitHub CI tests to include lowest-direct dependency resolution, as suggested for another package in
materialsproject/jobflow#640 (comment)

I think this would best be done in the post-merge workflow (called test-comprehensive) rather than the standard testing work flow, but I'm open to suggestions.

[abhardwaj73]

Hi Ryan, Looks like the post-merge workflow you mentioned is called post-process.yml.

In the PR I've added the following lines:

        version:
          - { python: "3.9", resolution: highest, extras: strict }
          - { python: "3.10", resolution: lowest-direct, extras: strict }
          - { python: "3.11", resolution: highest, extras: non-strict }
          - { python: "3.12", resolution: lowest-direct, extras: non-strict }

instead of
python-version: ['3.9', '3.10', '3.11']

as done in materialsproject/jobflow#640 (comment)