ci: update for cibuildwheel 3.1

[henryiii]

Description

Update for upstream fixes and bumps, mostly from 3.1.

[mhsmith]

Neither Android nor iOS have official wheels for NumPy yet, although iOS is getting close.

Unfortunately the sys_platform check won't work on either platform at the moment, because the pip --platform option doesn't affect environment markers (https://github.com/pypa/pip/issues/11664). Until this is fixed, we should probably change cibuildwheel to run pip within the cross-venv instead, as we did in Briefcase (https://github.com/beeware/briefcase/pull/2101).

@freakboy3742: FYI.

[mhsmith]

Unfortunately the sys_platform check won't work on either platform at the moment

This is fixed for Android by https://github.com/pypa/cibuildwheel/pull/2575. @freakboy3742 believes its actually OK on iOS.

[freakboy3742]

From the look of it, those iOS test failures are all because the test is trying to start a process (or, more specifically, trying to load _multiprocessing, which doesn't exist on iOS). I don't think there's any fix other than skipping those tests on iOS.