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

Flang triggers some OOM on Windows CI right now. This is disruptive to
MLIR and LLVM changes that don't touch Flang, as such we disable
building Flang on Windows only for these PR that don't touch flang. The
testing on Linux is unchanged, and the post-merge Windows testing is
still fully covering here.