[llvm] [CI][format] Explicitly pass extensions to git-clang-format (PR #95794)

[Aiden Grossman via llvm-commits]

boomanaiden154 wrote:

@ldionne This was causing a reasonably significant portion of formatting failures to not get caught. See #97060. I've reverted for now.

https://github.com/llvm/llvm-project/pull/95794