An annotated instance variable on super class is not documented when derived class has other annotated instance variables

[tk0miya]

Describe the bug
An annotated instance variable on super class is not documented when derived class has other annotated instance variables

To Reproduce
Steps to reproduce the behavior:

# example.py
class Foo:
    var1: int


class Bar(Foo):
    var2: int

# index.rst
.. automodule:: example
   :members:
   :undoc-members:
   :inherited-members:

Bar.var1 is not shown even if :inherited-members: option given.

Expected behavior
Both var1 and var2 are shown.

Your project
No

Screenshots
No

Environment info

• OS: Mac
• Python version: 3.8.2
• Sphinx version: HEAD of 3.x
• Sphinx extensions: sphinx.ext.autodoc