Stubgen creates instance methods instead of class variables for C extensions

Bug Report

We are in the process of adding .pyi stubs for PyICU. (https://gitlab.pyicu.org/)

The URegionType class, for example, is an enumeration. inspect.getmembers(icu.URegionType) lists [('CONTINENT', 3), ('DEPRECATED', 6), ('GROUPING', 5), ('SUBCONTINENT', 4), ('TERRITORY', 1), ('UNKNOWN', 0), ('WORLD', 2), ('__class__', <class 'type'>), ('__delattr__', <slot wrapper '__delattr__' of 'object' objects>), ...

CONTINENT and other class variables are generated in _icu_.pyi as if they were class methods.

To Reproduce

The problem might be specific to C extensions. If you want to recreate the problem on the PyICU code:

python setup.py build
cd build/lib.linux-x86_64-cpython-310
stubgen -p icu

Expected Behavior

_icu_.pyi should have contained

class URegionType:
    CONTINENT: Any
    DEPRECATED: Any
    GROUPING: Any
    SUBCONTINENT: Any
    TERRITORY: Any
    UNKNOWN: Any
    WORLD: Any

Actual Behavior

_icu_.pyi instead contains:

class URegionType:
    def CONTINENT(self, *args, **kwargs) -> Any: ...
    def DEPRECATED(self, *args, **kwargs) -> Any: ...
    def GROUPING(self, *args, **kwargs) -> Any: ...
    def SUBCONTINENT(self, *args, **kwargs) -> Any: ...
    def TERRITORY(self, *args, **kwargs) -> Any: ...
    def UNKNOWN(self, *args, **kwargs) -> Any: ...
    def WORLD(self, *args, **kwargs) -> Any: ...

Your Environment

• Mypy version used: 0.990
• Mypy configuration options from mypy.ini (and other config files): defaults/none
• Python version used: 3.10

Reproduce the issue with the provided PyICU build commands and inspect the stubgen path that classifies members from C extensions. Confirm the generated icu.pyi output for URegionType, then add coverage or a fix so CONTINENT and the other enumeration members are emitted as class variables rather than methods.