[llvm] Add GitHub workflow for check Python file formatting (PR #65482)

[Jonas Devlieghere via llvm-commits]

JDevlieghere wrote:

This is great! 

Regarding the discussion about making this part of CMake: I agree with Tobias. We don't do this for clang-format either and I don't really want a build/configure step to modify my source directory. I think a pre-commit hook or workflow makes a lot more sense.

https://github.com/llvm/llvm-project/pull/65482