[llvm] [CI] Disable flang from Windows pre-commit tests (PR #93485)

[Renato Golin via llvm-commits]

rengolin wrote:

> I agree with @joker-eph we should still build and test it when flang/ files are touched.

Agree. What's the right incantation to make that work in our CI?

https://github.com/llvm/llvm-project/pull/93485