B027 false positive with abc.abstractclassmethod

[Skylion007]

Adding an abstractmethod decorator does not make sense if an abstractclassmethod decorator is used instead:
When doing an automated fixes to the PyTorch codebase I ran into an issue in the wild:

class Foo(metaclass=abc.ABCMeta):
    @abc.abstractclassmethod
    def read(self): 
        pass

should not be flagged for instance (but currently is). This should be an easy exclusion to add to the rule and a good first issue.

[charliermarsh]

Just gonna fix this real quick.