Cannot infer type of generic attributes in `match` statements when inheritance is involved

Bug Report

mypy has trouble inferring the type of generic attributes in match statements when inheritance is involved.

This issue was encountered while investigating #13612

To Reproduce

from typing import Generic, TypeVar

T = TypeVar("T")


class Base(Generic[T]):
    ...

class A(Base[T]):
    x: T

    __match_args__ = ('x', )

    def __init__(self, x: T):
        self.x = x


a: Base[str] = A("foo")
reveal_type(a)  # Base[str] (correct)

match a:
    case A(b):
        reveal_type(b)  # Any (incorrect! Should be builtins.str)

Expected Behavior

The attribute on the last line above is revealed to be str

Actual Behavior

It is revealed to be Any

Your Environment

• Mypy version used: mypy-0.980+dev.b031f1c04e1ee4331e4d6957c7a9b727293328a9
• Mypy command-line flags: none
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.10.5
• Operating system and version: n/a