Add docstring to `ConcurrencyViolationError`

[Seelengrab]

This should cover the current usecases of this error.

[Seelengrab]

What is recorded in those files?

[vtjnash]

The source for the https://docs.julialang.org/en/v1/ pages

[Seelengrab]

I think it'd be good to have a dedicated "You're doing something weird with concurrency; if you see this error you most likely have a bug in your code" error, so yeah, having that listed there sounds good. I'll add it. Is there a specific section it should be listed in?

[gbaraldi]

Multithreading maybe?

[Seelengrab]

I'm not sure it's worth adding a whole big paragraph of prose though :/ If this were a personal project, I'd just have it in a reference list (kinda like here, except it'd only contain multi-threading related docstrings). It's not like there are big examples necessary for how to use it. We don't really have those kinds of section-specific lists in the manual, unfortunately.

[Seelengrab]

Alright, I've added a short blurb to the section on data races, which seemed like the most appropriate place ConcurrencyViolationError should be mentioned.

[Seelengrab]

Failures are due to not having a canonical place for the docstring-@ref of ConcurrencyViolationError. Do we have a place for multithreading docstrings to be shown that I can add this too?

[vtjnash]

Those seem to be split between docs/src/base/multi-threading.md and docs/src/base/parallel.md, with probably a preference towards the former for this, though either seems acceptable.

[Seelengrab]

Ok, I've added it to parallel.md, since the error is not exclusive to multithreading but for concurrency in general. Let's see if CI likes it now.

[Seelengrab]

Failures seem unrelated, so should be good to merge if the addition to the docs is ok.

[ViralBShah]

Should we merge?

[Seelengrab]

Like I said in May, if the failure is unrelated (and it seems like it is) and folks are fine with the wording, yes. It's just a doc change.