1.9 Regression: __hash__ method in attrs class is ignored

[Hnasar]

Bug Report
mypy is ignoring a manually-written __hash__ method in an attrs class.
Bisect points to 91be285 causing the regression. cc @Tinche
Possibly reported already in a comment here? #16556 (comment)

To Reproduce

import attrs
from typing import reveal_type

@attrs.define()
class A():
    name: str = attrs.field()
    def __hash__(self) -> int:
        return hash(self.name)

reveal_type(A.__hash__)

Expected Behavior

$ py -m mypy --strict foo.py  # 1.8
foo.py:10: note: Revealed type is "def (self: foo.A) -> builtins.int"
$ py foo.py
Runtime type is 'function'

Actual Behavior

$ py -m mypy --strict foo.py  # 1.9
foo.py:10: note: Revealed type is "None"
$ py foo.py
Runtime type is 'function'

Your Environment

• Mypy version used: 1.9.0
• Mypy command-line flags: n/a
• Python version used: 3.12
• attrs version: 23.2.0

[Tinche]

I'll take this.