mypy throws wrong assignment error in dataclasses.__post_init

[Felixoid]

Bug Report

mypy fails to proceed a known dataclass field, considering it's a list[object], see the reproduce script and the output

To Reproduce

from dataclasses import dataclass
from pathlib import Path
from typing import Sequence, Union


@dataclass
class TestCase:
    files: Union[Sequence[str], Sequence[Path]]

    def __post_init(self) -> None:
        self.files = sorted(
            self.files, key=lambda x: str(x).rsplit("/", maxsplit=1)[-1]
        )

Expected Behavior

There shouldn't be errors

Actual Behavior

> mypy .
mypy_fail.py:11: error: Incompatible types in assignment (expression has type "list[object]", variable has type "Sequence[str] | Sequence[Path]")  [assignment]

Your Environment

• Mypy version used: mypy 1.14.0 (compiled: no)
• Mypy command-line flags: none
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.13.2

In the scope of ClickHouse/ClickHouse#76679