Fix ErrorsWithCodes().__class__ return value

[ilivans]

Description

Fix ErrorsWithCodes().__class__ value - it should be a class rather than a string like "[__class__] .." before.
It's critical for functions which try to inference the class of an object, i.e. isinstance
I personally encountered the issue using rollbar which collects all the visible variables and tries to serialize those. In case of ErrorsWithCodes() it failed during isinstance(o, collections.abc.Mapping) check.

I ran all the tests using Python 3.8, Ubuntu 19.04, no spacy models preinstalled.
spacy is installed with pip install -e path_to_repo.

FAILED spaCy/spacy/tests/lang/fa/test_noun_chunks.py::test_noun_chunks_is_parsed_fa - Failed: DID NOT RAISE <class 'ValueError'>
======================== 1 failed, 1709 passed, 890 skipped, 49 xfailed, 1 xpassed, 4 warnings in 69.88s (0:01:09) =========================

*The failed test case fails without my change too

Types of change

A bug fix

Checklist

• I have submitted the spaCy Contributor Agreement.
• I ran the tests, and all new and existing tests passed.
• My changes don't require a change to the documentation, or if they do, I've added all required information.

[adrianeboyd]

Huh, I don't know why the CI didn't fail before on that test, very weird, but thanks for the quick catch!