[llvm] [Github] Do not label clang-format files as clang (PR #66388)

[Vlad Serebrennikov via llvm-commits]

Endilll wrote:

> This LGTM, but you should get an OK from @AaronBallman

This takes us where we are in bug tracker, i.e. `clang` label doesn't duplicate `clang:*` and `clang-*` labels.
If this gets rejected, I think we're in trouble.

https://github.com/llvm/llvm-project/pull/66388