Issue initialising dataclass with getters and setters

When using mypy with a dataclass that includes getters and setters it throws an error. It returns Name 'byr' already defined on line 5.

To Reproduce

To reproduce use mypy with this script:

@dataclass
class Passport:
    byr: int

    @property
    def byr(self) -> int:
        return self._byr

    @byr.setter
    def byr(self, value) -> None:
        if int(value) < 1920 or int(value) > 2002:
            raise Exception("Birth year must be between 1920 and 2002")
        self._byr = int(value)

Expected Behavior

I would have expected it to accept this, as this seems to be a standard way to handle getters and setters.

Your Environment

• Mypy command-line flags: python -m mypy my.py
• Python version used: 3.9.0
• Operating system and version:

提供されたdataclassから始め、python -m mypy my.pyを実行して重複名エラーを再現します。dataclassesとproperty getters/settersがどのように解析されるかを追跡し、その後、このパターンがエラーなしで受け入れられることを示すリグレッションテストを追加します。