Test Python 3.12.

[joaander]

Description

Test on Python 3.12. Also limit the number of jobs that run on limited macOS and windows runners.

Motivation and Context

• Ensure that dashboard works with Python 3.12.
• Previously, the actions workflow ran the full matrix of tests on all 3 operating systems. This redundant testing adds significantly to the total time needed to test a push as GitHub Actions provides only a limited number of free macOS and Windows runners.

This PR limits macos and windows to 1 job each on the newest version of python and tests the full matrix on Linux.

Checklist:

• I am familiar with the Contributing Guidelines.
• I agree with the terms of the Contributor Agreement.
• The changes introduced by this pull request are covered by existing or newly introduced tests.
• The package documentation and framework documentation in signac-docs are up to date with these changes.
• I have updated the changelog and added any related issue and pull request numbers for future reference.

[codecov]

Codecov Report

Merging #205 (96c69d9) into main (4f6a083) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #205   +/-   ##
=======================================
  Coverage   70.02%   70.02%           
=======================================
  Files          21       21           
  Lines         884      884           
  Branches      159      159           
=======================================
  Hits          619      619           
  Misses        220      220           
  Partials       45       45           

[joaander]

Correction: Windows runners are not limited (https://docs.github.com/en/actions/learn-github-actions/usage-limits-billing-and-administration). However, Windows runners are slower than the Linux runners, so Linux is preferred for the full matrix.

[cbkerr]

Okay with this as-is but see note on testing oldest versions?