[llvm] [Github] Make PR formatting job only run with C/C++ changes (PR #69556)

[Tobias Hieta via llvm-commits]

tru wrote:

Please revert or extend since this now doesn't run on python files. The code formatter runs both formatting which is why I opted to not have a filter here since that means we need to maintain several lists of extensions. 

https://github.com/llvm/llvm-project/pull/69556