False positive E1102 when adding a non-callable attribute to object

[exquo]

Steps to reproduce

'test'.startswith('t')
o = object()
x = 42
if o is x:
    o.startswith = None

Current behavior

$ pylint -E file.py
************* Module file
file.py:1:0: E1102: 'test'.startswith is not callable (not-callable)

Expected behavior

No errors.

pylint --version output

pylint 2.7.2
astroid 2.5.1
Python 3.7.3 (default, Jul 25 2020, 13:03:44)
[GCC 8.3.0]

Pylint probably reasons like this: str is a subclass of object; object's attribute is assigned to non-callable; thus, str's attribute by the same name should be non-callable. I can see the logic here, but the error is reported on the very first line, before the attribute has the chance to get re-assigned.

By itself, the above example code is not very meaningful. I'm reporting it because this seems to be the underlying cause of #3970 (comment). Also, it might manifest itself in other, more practical scenarios than the example above.