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

[Kiran Chandramohan via llvm-commits]

kiranchandramohan wrote:

Thanks @joker-eph. 
What would be a reasonable state for the Windows Flang builds to be re-enabled for LLVM and MLIR? Demonstration of One week or month without OOM in the flang patches (where the windows flang build and tests run)?

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