False-positive of unused-private-member with class reference

[yumasheta]

Bug description

Consider the following code snippet:

"""p.py"""

class UnusedPrivateMember:
    """unused-private-member (W0238)"""

    @staticmethod
    def __private_method():
        """Is private and does nothing."""

    @classmethod
    def use_private_method(cls):
        """Calls private method."""
        cls.__private_method()

Configuration

No response

Command used

pylint p.py

Pylint output

W0238: Unused private member `UnusedPrivateMember.__private_method()` (unused-private-member)

Expected behavior

Calling a private static method only on cls (reference to class) in a classmethod produces false positive: unused-private-member.

#4782 recently fixed some issues regarding the usage of private members on the class name. This one seems to have slipped through.

Thanks.

Pylint version

pylint 2.10.0-dev0
astroid 2.6.6
Python 3.9.6 (default, Jun 30 2021, 10:22:16) 
[GCC 11.1.0]

### OS / Environment

_No response_

### Additional dependencies

_No response_

[cdce8p]

/CC: @yushao2

[yumasheta]

I think the fix is easier than I thought. Though, please look at my PR, as I never used astroid before.