The recently announced mac1.metal instance type on AWS is interesting. I can imagine it would be very useful for building iOS apps and the like that require a Mac or running site tests with the Safari browser.
The aren’t running the new M1 chip, but are on some pretty decent Intel i7 processors, so they should be plenty fast. I don’t suppose you care too much about power consumption if it’s in the cloud.
I couldn’t find any pricing, but if the instances spin up quickly, it shouldn’t take very long for a CI/CD pipeline to run on them.