[llvm] [CI] Disable flang from pre-commit tests when Flang files are not touched (PR #93485)

[Valentin Clement バレンタイン クレメン via llvm-commits]

clementval wrote:

> > So is this disabling both linux and windows pre-commit testing?
> 
> Yes but only on PR that don't touch flang directly. That is a PR that would only touch other projects (llvm/mlir/clang) used to to trigger testing of Flang since they can potentially break it.

It would be nice to keep flang testing when MLIR is changed since it relies a lot on it. 

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