Special reference __class__ is considered undefined in nested lexical scope.

[emcd]

Reproducer

class Something:
    def _enclose( ):
        def __init__( self ):
            print( __class__ )
        return __init__
    __init__ = _enclose( )

something = Something( )

Steps to reproduce

1. Run pylint --score=no --reports=no --enable=all --disable=missing-module-docstring,missing-class-docstring,multiple-statements,too-few-public-methods,no-method-argument,unused-argument on the reproducer above.
2. Note that Pylint complains about __class__ being an undefined variable.
3. Run the reproducer in a Python interpreter and note that it executes correctly.

Current behavior

$ pylint --score=no --reports=no --enable=all --disable=missing-module-docstring,missing-class-docstring,multiple-statements,too-few-public-methods,no-method-argument,unused-argument pylint-bugs/nested_dunder_class.py 
************* Module nested_dunder_class
pylint-bugs/nested_dunder_class.py   4,19 [undefined-variable] Undefined variable '__class__'

$ python3 pylint-bugs/nested_dunder_class.py
<class '__main__.Something'>
$

Expected behavior

No error since this is valid Python.

pylint --version output

$ pylint --version
pylint 2.6.0
astroid 2.4.2
Python 3.6.12 (default, Nov  8 2020, 15:40:05) 
[GCC 5.4.0 20160609]