does not work with PyGObject 3.7.2: AttributeError: 'gi.repository.GObject' object has no attribute 'GObjectMeta'

aptdaemon currently does some curious hack with subclassing from GObject.GObjectMeta, which stops working with PyGObject 3.7.2:

$ PYTHONPATH=.:~/upstream/pygobject ./gtk3-demo.py
Traceback (most recent call last):
  File "./gtk3-demo.py", line 37, in <module>
    import aptdaemon.client
  File "/home/martin/upstream/aptdaemon/aptdaemon/client.py", line 70, in <module>
    class MemoizedMixInMeta(MemoizedTransaction, GObject.GObjectMeta):
  File "/home/martin/upstream/pygobject/gi/module.py", line 316, in __getattr__
    return getattr(self._introspection_module, name)
  File "/home/martin/upstream/pygobject/gi/module.py", line 135, in __getattr__
    self.__name__, name))
AttributeError: 'gi.repository.GObject' object has no attribute 'GObjectMeta'

(This is also thrown by the tests).

I'm afraid I don't fully understand what MemoizedMixInMeta and MemoizedMixIn are supposed to do; it can certainly be fixed to work with current PyGObject, or preferrably with not using the "GObjectMeta" internal implementation detail in the first place; however, this class is used exactly once, so it seems easier to just move the overridden __call__() method into AptTransaction and drop the black magic?