[llvm] [CI] Disable Flang from pre-commit tests when Flang files are not touched on Windows Only (PR #93729)

[Mehdi Amini via llvm-commits]

joker-eph wrote:

I don't have much to add to @rengolin here, I would start by looking at the "expensive" files in flang and try to split them maybe? Someone with MSVC 2019 could try to profile the build to find these files that are memory hungry maybe?

https://github.com/llvm/llvm-project/pull/93729