Migrate to GitHub Actions

[KodrAus]

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[KodrAus]

While I'm here we should migrate those compile tests to trybuild 👀

[smoelius]

While I'm here we should migrate those compile tests to trybuild eyes

May I ask, what benefit would this provide? (This is a serious question, BTW.)

[KodrAus]

@smoelius There are two main ones I'm interested in:

1. Not needing to set up a separate project to run compile tests, since they're what exercises most of the library. trybuild has a simpler API to work with.
2. We might be able to get rid of some hacks we've accumulated to work around complexities in invoking Cargo the way these libraries do. We've had to shim lazy-static to make the old tests work because it's been a dependency of the compiler.

[smoelius]

Thanks, @KodrAus. I would be curious to see what those changes would look like.