[llvm] [Workflow] Expand code-format-helper.py error reporting (PR #69686)

[Ryan Prichard via llvm-commits]

rprichard wrote:

> > One of my test PRs was supposed to fail C++ and Python formatting, but instead it only failed on C++, and it reproduced the failure mode where `darker` simply ignores code formatting errors:
> > https://github.com/rprichard/llvm-project/actions/runs/6592874295/job/17914345865?pr=4
> > Apparently darker is succeeding with no stdout/stderr output?
> 
> Hmm that doesn't seem right. I am pretty sure I had it failing with the right code before. Are you sure this isn't related to your changes?

I don't think so? `darker` did the same thing to me on an actual PR, which motivated me to try and expand the error reporting. #69274. Maybe it's not checking newly added files?... I should see if I can get this to reproduce.


https://github.com/llvm/llvm-project/pull/69686