singledispatchmethod decorated method fails with unknown method register

I played with an update of mypy from 0.931 to 0.971. The new version fails with error: "Callable[..., bool]" has no attribute "register"
The code is written oddly because of known Python issue https://bugs.python.org/issue41987 , the interpreter has no issue with it.

from functools import singledispatchmethod

class Issue:
  @singledispatchmethod
  def __contains__(self, other) -> bool:
      return True

@Issue.__contains__.register
def _(self, other: Issue) -> bool:
    return False

$ mypy issue.py
issue.py:12: error: "Callable[..., bool]" has no attribute "register"
Found 1 error in 1 file (checked 1 source file)

Beginne damit, den issue.py-Reproduzierer mit mypy auszuführen und nachzuverfolgen, wie functools.singledispatchmethod modelliert wird, insbesondere den Zugriff auf Issue.contains.register. Die Korrektur ist vollständig, wenn dieses Beispiel ohne den gemeldeten Fehler die Typprüfung besteht und die Testabdeckung die Regression verhindert.