[llvm] [Github][CI] Add Windows Premerge Job for Testing (PR #122661)

[Aiden Grossman via llvm-commits]

boomanaiden154 wrote:

I'm going to land this now so that we can catch any infrastructure issues sooner rather than later. If anyone has any post-commit feedback, please leave it here (or on the commit) and I will address it in a future PR.

https://github.com/llvm/llvm-project/pull/122661