Overlapping unions creates issues with inference

[yilinwei]

• version: 7.3.0

When creating a union which has overlapping types, the inference fails. Either this should throw an error, or it should be inferred correctly.

from typing import TypeVar, Union, Iterable, List

T = TypeVar("T")

def foo(test: Union[T, List[T]]):
    pass

foo([1]) # Fails with incompatible type List[<nothing>]

• Example of misuse here

[ilevkivskyi]

Duplicate of #6417