Support MacOS 14 github runner (which is now default)

[notatallshaw]

Github's macos-14 runner is rolling out as macos-latest over the following weeks: https://github.blog/changelog/2024-04-01-macos-14-sonoma-is-generally-available-and-the-latest-macos-runner-image/

macos-14 no longer includes SVN by defeault: https://github.com/actions/runner-images/blob/main/images/macos/macos-14-Readme.md Where as macos-12 (the previous macos and the one pip runners still appear to be on) did: https://github.com/actions/runner-images/blob/main/images/macos/macos-12-Readme.md

When pip's macos-latest runners get updated to macos-14 CI tests will currently fail due to lack of subversion. This PR preempts that by explicitly installing SVN.

I have a secondary PR to explictly support both x86 and M1 runners: https://github.com/pypa/pip/pull/12593

[notatallshaw]

Pip's macos-latest runner is now macos-14 causing pip CI to fail: https://github.com/pypa/pip/actions/runs/8825862850/job/24230722241

I've removed Python 3.8 and 3.9 in this PR to fix CI with macos-latest.

[notatallshaw]

Going to close this as I am not in a position to be able to test and fix the failing 3.8 and 3.9 tests on MacOS Latest (M1).