npub13385x9zu5czskpud40ukzc2m0hhjr9f0kckk79uq293qxty78vrsyhe8jk (npub1338…e8jk) I don't specifically know how GitHub is handling it, but it's usually on real hardware. AWS provides macOS compute via shared minis, for example:
https://aws.amazon.com/ec2/instance-types/mac/