Import used by type annotation inside __new__ is considered unused

An import used by a type annotation inside __new__() in a metaclass is considered unused by flake8/pyflakes/whatever component.

e.g. given:

    from django.db.models import Model

    class SomeMetaclass(type):
        def __new__(mcs, name, bases, attrs):
            model_class_attrs: [(str, Model,)] = []
            model_class_attrs.clear()
            return super().__new__(mcs, name, bases, attrs)

Running flake8 results in the error:

    example.py:1:1: F401 'django.db.models.Model' imported but unused

Versions:

Python 3.6
flake8 3.3.0
mccabe 0.6.1
pycodestyle 2.3.1
pyflakes 1.5.0