[ci] Build and test mac14 with the minimal option activated

[dpiparo]

This will compensate for the slowness of the runners.

[github-actions]

Test Results

2 511 tests   2 511 ✅  3h 57m 1s ⏱️
    1 suites      0 💤
    1 files        0 ❌

Results for commit 3bef1cf.

♻️ This comment has been updated with latest results.

[guitargeek]

Interesting idea! I have two questions:

• Can this PR maybe wait for [cppyy] Review xfail'ed tests #20906? I'm doing a large-scale review of which cppyy tests are actually passing on which platforms, so it would be good to keep the full mac14 configuration until this is done. I could revert your proposed change in that PR for testing, but then I still would not have a complete mac14 reference in the nightlies and might not be able to tell apart failures in my PR from potential regressions in master.
• What's the strategy for the release branches, including the upcoming 6.40 branch? We enable the full build there?