Enums with only descriptor members should not be final

[decorator-factory]

Bug Report

If all members of an Enum class are descriptors, the class should still be subclassable.

Quote from the Python documentation:

The rules for what is allowed are as follows: names that start and end with a single underscore are reserved by enum and cannot be used; all other attributes defined within an enumeration will become members of this enumeration, with the exception of special methods (__str__(), __add__(), etc.), descriptors (methods are also descriptors), and variable names listed in _ignore_.

This would also match the behaviour of Pyright (1.1.234)

To Reproduce

1. Install mypy==0.941
2. Run mypy on this code:

import logging
from enum import Enum


class LoggedAccess:
    def __set_name__(self, owner, name):
        self.public_name = name
        self.private_name = '_' + name

    def __get__(self, obj, objtype=None):
        value = getattr(obj, self.private_name)
        logging.info('Accessing %r giving %r', self.public_name, value)
        return value

    def __set__(self, obj, value):
        logging.info('Updating %r to %r', self.public_name, value)
        setattr(obj, self.private_name, value)


class Foo(Enum):
    thing = LoggedAccess()

    
class Bar(Foo):
    x = 42

Expected Behavior

No errors - this runs just fine

Actual Behavior

 error: Cannot extend enum with existing members: "Foo"

Your Environment

• Mypy version used: 0.941