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

[Tobias Hieta via llvm-commits]

tru wrote:

> May be this should be part of the build as `Clang-format` in `polly`? Same could be done for Python linters (`Flake8`, `PyLint`, `MyPy`).

Not sure what you mean. I am not familiar with what polly does? We seldom "build" for python scripts. 

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