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

[Tobias Hieta via llvm-commits]

tru 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?

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