Bump macos runner version

[da-woods]

macos-13 is being removed relatively soon

https://github.blog/changelog/2025-07-11-upcoming-changes-to-macos-hosted-runners-macos-latest-migration-and-xcode-support-policy-updates/

[da-woods]

I think something in the project setting explicitly requires some runners called macos-13 to complete, so I may not be able to merge this...

[da-woods]

There's a bit of a mess to sort out here with line_profiler (including that we're not running the test on Python >= 3.10)

[da-woods]

Doesn't immediately look like this is going to work. I'll close this PR for now and come back to it some other time

[scoder]

I think something in the project setting explicitly requires some runners called `macos-13` to complete

To allow auto-merge, Github requires an explicit list of CI jobs that need to succeed before the merge. I listed a couple of macos jobs there which get in the way if you change the macos image versions. They are not automatically adapted, I have to replace them in the job list manually. Just tell me and I'll change the settings.

[da-woods]

Currently we're blocked by the line_profiler tests. Updating to the newer OS X image means that line_profile needs to compile manually and the old version we rely on doesn't build with recent Cython (and doesn't have a suitably restrictive version pin). I'm sure it's fixable, but it's probably not worth the effort.

It looks like line_profile have very recently fixed their Cython compatibility (pyutils/line_profiler#352) so as soon as that makes into into a release we should be able to use that.

So I think we just wait for that to happen before changing any OS X runners (at which point I'll need you to change the explicit list of jobs)