[libcxx] [llvm] [libc++][WIP] Move to Github hosted builders (PR #109720)

[Aiden Grossman via llvm-commits]

boomanaiden154 wrote:

> This won't work because we can't run containers on images within the container image that the bot runs in.

This is switching over to the Github Actions runners which are hosted in VMs, so can run containers just fine.

https://github.com/llvm/llvm-project/pull/109720