Instance attributes are omitted with autosummary

[Chilipp]

This issue is a followup of #7948. Sorry, I forgot to open it.

Is your feature request related to a problem? Please describe.
Instance attributes are omitted when using the autosummary, as they cannot be imported. Consider the following class

# contents of test_mod.py

class Test:
    """Test class"""

    #: int. Some class attribute
    test: int = 1

    def __init__(self, a: int):
        #: int. An instance attribute
        self.a = 1

autodoc via

.. autoclass:: Test
    :members:

will document the a attribute, but autosummary via

.. autosummary::

    Test.a
    Test.test

won't.

Describe the solution you'd like
Instance attributes should be documented, too

Describe alternatives you've considered
it did work before 1dcfc44, i.e. for sphinx<3.1 (although the documentation was omitted).

Additional context

• add item even if it could not be imported #7948
• files to reproduce the issue (including page build) test.zip
• Screenshot of index.html
  

[Chilipp]

@tk0miya, I cannot add labels or milestones here, but nonetheless already closed #7948

[tk0miya]

Okay, I'll try to fix this if I have time until the next release.

[Chilipp]

Absolutely great! Thanks a lot @tk0miya!