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

[Tobias Hieta via llvm-commits]

tru wrote:

> > LGTM, I assume this has been tested somehow right?
> 
> Unfortunately, it still needs to be tested somehow. I did notice that you had some way to demo it on [tru#8](https://github.com/tru/llvm-project/pull/8).

Yes, the way I tested it was that I pushed my changes to a branch in my fork (i.e. `formatter`), then I created a new branch based on `formatter` called something like `test_formatter` and do a small change where the formatted would fail. Then I would open a PR from `test_formatter` towards `formatter` and it will run the code.

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