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

[via llvm-commits]

cor3ntin wrote:

I had a chat with Aaron yesterday, he was favorable to merge that, so I'll go ahead.
We had a chat about whether a more general solution was needed, and if so we can implement something better than negative matches, but this require a longer discussion (ad quite a bit more work) and we might not have consensus to do so. I wrote up my thoughts here https://discourse.llvm.org/t/hows-it-going-with-pull-requests/73467/27?u=cor3ntin

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