Return type of property setters is not checked

Example code:

class Banana:
    @property
    def size(self) -> int:
        return 42

    @size.setter
    async def size(self, value: int, /) -> None:
        print(f"set value to {value!r}")

b = Banana()
b.size = 42

I expected mypy to complain that the setter function doesn't return None and returns Coroutine[Any, Any, None] instead. Similarly, if the setter is a non-async function returning e.g. str or int, no error is reported.

Environment

• Mypy version used: 1.19.1
• Mypy command-line flags: --strict
• Python version used: 3.14

The issue names no source file or test. Reproduce the property-setter examples with mypy 1.19.1 and --strict, then trace the type-checking path for property setters. Add regression coverage for async and non-None setters, with diagnostics confirming their return types are checked.