Silence flake8-bugbear

[sobolevn]

I don't think that

/src/typing_extensions.py:434:5: B024 _ProtocolMeta is an abstract base class, but it has no abstract methods. Remember to use @AbstractMethod, @abstractclassmethod and/or @abstractproperty decorators.

is even correct, because in this case we create a new metaclass in the ABC chain.
But, I guess the only other option is to complete ignore this violation.