Minimise PR wheel build times #109

Re-apply Fergus's change to spread out wheels python versions over platforms on the case of PR builds: https://github.com/PalamaraLab/PrepareDecoding/blob/78018ec6aa6b0359c54ae55fa5b0d5b6cd8e285c/.github/workflows/python-wheels.yml#L52

The motivation for that change was to reduce build times on macos agents on private agents. That is not such an issue on threads as it is public, but there have been a few spikes in threads macos build costs and this change keeps threads in line with other projects.

This change was also made to arg-needle-lib here https://github.com/PalamaraLab/arg-needle-lib_dev/issues/45