Inheriting from NamedTuple causes "Overloaded function signatures 1 and 2 overlap with incompatible return types" #18562

Bug Report

When two classes inherit from NamedTuple, I get an overlap error when I want to overload based on their type.

To Reproduce

https://mypy-play.net/?mypy=latest&python=3.12&gist=38e025ef049b6a1121cdd92c998e84a9

from typing import overload, NamedTuple

class A(NamedTuple):
    pass

class B(NamedTuple):
    pass

@overload
def frobnicate(arg: A) -> A: ...

@overload
def frobnicate(arg: B) -> B: ...

def frobnicate(arg: A | B) -> A | B:
    if isinstance(arg, A):
        return A()
    elif isinstance(arg, B):
        return B()
    else:
        raise TypeError()

Expected Behavior

I expect this to not cause an error. It does not report an error if A and B inherit from tuple, dict or object instead.

Actual Behavior

error: Overloaded function signatures 1 and 2 overlap with incompatible return types [overload-overlap]

Your Environment

• Mypy version used: 1.14.1
• Mypy command-line flags: (playground)
• Mypy configuration options from mypy.ini (and other config files): (playground)
• Python version used: 3.12