blhsing

The workaround aside, what is the reason, technical or conceptual, behind why these mypy classes have to explicitly disallow inheritance by interpreted subclasses in the first place? It otherwise seems...

I think this is a good time to add [`test`](https://docs.python.org/3/library/test.html) to `sys.stdlib_module_names` for developers who happen to name their test scripts as `test.py` but actually want to run test suites...