Fix CI for Python 3.7 on macOS by only running these tests on macos-13

[JeanChristopheMorinPerso]

GitHub rolled out macos-14 and made it the latest (macos-latest). The macos-14 image runs on Apple Silicon.

Tests for Python 3.7 on macOS were failing because Python 3.7 was not officially supported on M1s.

This PR changes our CI so that Python 3.7 tests run on macos-13 (Intel CPUs).

[codecov[bot]]

Codecov Report

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

Project coverage is 58.30%. Comparing base (36e0537) to head (16b7428). Report is 8 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1750 +/- ## ========================================== + Coverage 58.29% 58.30% +0.01% ========================================== Files 126 126 Lines 17159 17159 Branches 3505 3505 ========================================== + Hits 10002 10004 +2 + Misses 6493 6492 -1 + Partials 664 663 -1 ```

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