[llvm] [GitHub][CI] Run clang-format natively in ci-ubuntu container (PR #161073)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 commented:

We probably shouldn't be dropping `setup-python`. Removing the pip dependency cache (even if it doesn't hit unless it has been warmed on a PR) is probably going to be a significant regression.

https://github.com/llvm/llvm-project/pull/161073