Descriptors don't work with `TypeGuard`

Bug Report

The tool doesn't correctly interpret TypeGuard in the context of a descriptor.

To Reproduce

mypy-play.net gist

from __future__ import annotations

from typing import *
from typing_extensions import (
        TypeGuard,
        )

class SomeDescriptor:
    # simplified: no @overload for obj=None, klass=<type ...>
    def __get__(
            self, obj: object, klass: Optional[Type[object]] = None
            ) -> TypeGuard[DerivedClass]:
        return isinstance(obj, DerivedClass)

class BaseClass:
    described = SomeDescriptor()

class DerivedClass(BaseClass): pass


def problem(instance: BaseClass) -> None:

    if instance.described:
        reveal_type(instance)  # BaseClass      (expected: DerivedClass)
    else:
        reveal_type(instance)  # BaseClass      (correct)


def contrast(descr: SomeDescriptor, instance: BaseClass) -> None:

    if descr.__get__(instance):
        reveal_type(instance)  # DerivedClass   (correct)
    else:
        reveal_type(instance)  # BaseClass      (correct)

Expected Behavior

In problem(), the type of instance should be narrowed when instance.described is truthy.

Actual Behavior

While mypy understands that a TypeGuard returns a bool, it doesn't narrow the type when the TypeGuard returns True.

Your Environment

• Mypy version used: 1.8.0
• Mypy command-line flags: none
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.8, 3.12

Inizia con la riproduzione collegata in mypy-play e confronta il comportamento di TypeGuard in problem() con la chiamata diretta funzionante a get in contrast(). Segui il percorso di narrowing basato sui descrittori e verifica che instance venga ristretto a DerivedClass nel ramo vero, mentre il ramo falso rimanga BaseClass.