Pylint 2.9.4 failure for 'Subscript' object has no attribute 'attrname'

[gmcluhan]

Steps to reproduce

1. Run pylint against the code below

import subprocess

if index == 0:
    pobjs[index] = subprocess.Popen(
        commd, stdout=subprocess.PIPE, stderr=subprocess.PIPE
    )

Current behavior

Pylint is failing to properly lint this file.

Exception on node <Assign l.51 at 0x7f1c81969100> in file 'our_file.py'
     multiprocessing.pool.RemoteTraceback: 
     """
     Traceback (most recent call last):
       File "/.pyenv/versions/3.9.0/lib/python3.9/multiprocessing/pool.py", line 125, in worker
         result = (True, func(*args, **kwds))
       File "/workspace/.tox/lint39/lib/python3.9/site-packages/pylint/lint/parallel.py", line 69, in _worker_check_single_file
         _worker_linter.check_single_file(name, filepath, modname)
       File "/workspace/.tox/lint39/lib/python3.9/site-packages/pylint/lint/pylinter.py", line 994, in check_single_file
         self._check_file(
       File "/workspace/.tox/lint39/lib/python3.9/site-packages/pylint/lint/pylinter.py", line 1035, in _check_file
         check_astroid_module(ast_node)
       File "/workspace/.tox/lint39/lib/python3.9/site-packages/pylint/lint/pylinter.py", line 1172, in check_astroid_module
         retval = self._check_astroid_module(
       File "/workspace/.tox/lint39/lib/python3.9/site-packages/pylint/lint/pylinter.py", line 1217, in _check_astroid_module
         walker.walk(ast_node)
       File "/workspace/.tox/lint39/lib/python3.9/site-packages/pylint/utils/ast_walker.py", line 77, in walk
         self.walk(child)
       File "/workspace/.tox/lint39/lib/python3.9/site-packages/pylint/utils/ast_walker.py", line 77, in walk
         self.walk(child)
       File "/workspace/.tox/lint39/lib/python3.9/site-packages/pylint/utils/ast_walker.py", line 77, in walk
         self.walk(child)
       [Previous line repeated 3 more times]
       File "/workspace/.tox/lint39/lib/python3.9/site-packages/pylint/utils/ast_walker.py", line 74, in walk
         callback(astroid)
       File "/workspace/.tox/lint39/lib/python3.9/site-packages/pylint/checkers/refactoring/refactoring_checker.py", line 1352, in visit_assign
         self._append_context_managers_to_stack(node)
       File "/workspace/.tox/lint39/lib/python3.9/site-packages/pylint/checkers/refactoring/refactoring_checker.py", line 1416, in _append_context_managers_to_stack
         else assignee.attrname
     AttributeError: 'Subscript' object has no attribute 'attrname'
     """

Expected behavior

This should pass, it only fails in our Python 3.9 environment. It passes in 3.8.

pylint --version output

Result of pylint --version output:

2.9.4

[cdce8p]

I can reproduce it. It's likely caused by #4721. @DudeNr33 would you mind taking a look?

[DudeNr33]

Will look at it as soon as possible.

[cdce8p]

@DudeNr33 Thank you! 🐬