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

[via llvm-commits]

cor3ntin wrote:

@tstellar @Endilll This is mostly a clutch. if we want to support `clang:foo` not adding `clang`, I think in the long run we will have to fork the action and adding that ourselves. Expressing everything in terms of negative regex is just way too brittle.

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