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

[Renato Golin via llvm-commits]

rengolin wrote:

> I think is should be removed from the description to avoid confusion. The current issue is OOM while building Flang on Windows, which is not the issue the Discourse thread was created for (worth a new thread?)

Reworded the title and description of the PR to avoid confusion. Should be clear now.

@joker-eph @tstellar

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