Installing polychord on Github Actions on macos

[steven-murray]

Hi, I'd like to run CI on my application that depends on polychord on both macos and linux. The linux version is installing fine, but I can't seem to get the macos version to install at all. It keeps trying to use f77 as the fortran compiler, and I don't understand why. Have you been able to get it to install on macos on Github Actions?

[williamjameshandley]

This is hopefully something which will be fixed with the cmake #76 build, which generally makes os install substantially easier. Feel free to test out that branch/contribute to that PR if you find that it needs adjustment.