stub for sklearn.datasets.load_iris is missing a return type option

[egerlach]

The Returns section of the docstring for sklearn.datasets.load_iris() has two options:

1. An sklearn.utils.Bunch, if return_X_y is False
2. A tuple[ndarray, ndarray] if return_X_y is True

The type stub for the function is

def load_iris(*, return_X_y: bool = False, as_frame: bool = False) -> tuple[Bunch, tuple]: ...

but I believe it should be:

def load_iris(*, return_X_y: bool = False, as_frame: bool = False) -> Bunch | tuple[ndarray, ndarray]: ...

or at least:

def load_iris(*, return_X_y: bool = False, as_frame: bool = False) -> Bunch | tuple: ...

which might be all we can get with parsing.

This might not be the only case of this in the codebase, but unfortunately I just have enough time to write this ticket. Normally I like to come with a bit more information, sorry about that.