[llvm] [hlsl] Pin hlsl-test-all resusable workflow to main branch (PR #122518)

[Chris B via llvm-commits]

https://github.com/llvm-beanz approved this pull request.

I’m good with these tradeoffs. I don’t expect this workflow to change too often in significant ways, and since it is only a small part of the community depending on it we can make do with the challenges testing it.

Thank you @tstellar for your help getting this working!

https://github.com/llvm/llvm-project/pull/122518