[llvm] [CI][format] Explicitly pass extensions to git-clang-format (take 2) (PR #98227)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 approved this pull request.

LGTM.

I'll try and keep an eye on this over the next couple days after this lands to see if something drastically changes, but if the basics work, we should be good.

At some point I would like proper testing for the CI infrastructure, but haven't figured out how to do pieces of it. Hopefully I can spend some time on that soon.

https://github.com/llvm/llvm-project/pull/98227