mypy should check qualname (and other special dunders) #20821

Bug Report

Noticed when playing with #20819. When you assign an int to __qualname__, Python raises a TypeError but mypy itself doesn't.

To Reproduce

class X:
    __qualname__ = 5

Expected Behavior

Error.

Actual Behavior

No error.

Your Environment

Reproduced in mypy-play

• Mypy version used: 1.19.1
• Mypy command-line flags: N/A
• Mypy configuration options from mypy.ini (and other config files): N/A
• Python version used: 3.12