Restrict MacOS builds to fewer Python versions

[iustin]

Per https://github.com/iustin/pyxattr/actions/runs/7778373717, not all versions are available on MacOS 14, so restrict to a smaller set. I don't think that extensive (across Python versions) on MacOS brings much, if the base Linux job does that.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (2c683f4) 78.75% compared to head (dafb534) 78.75%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #45 +/- ## ======================================= Coverage 78.75% 78.75% ======================================= Files 1 1 Lines 480 480 Branches 78 78 ======================================= Hits 378 378 Misses 63 63 Partials 39 39 ```

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