Wrong type inferred when "not in" narrowing Any 

The revealed type here is `str | None`, which doesn't make sense:
```py
from typing import Any

def f(x: Any) -> None:
    if x is not None and x not in ["x"]:
        return
    reveal_type(x)  # "str | None"
```
The behavior was changed in ed0cd4acba02ed19b1cf18ac0ac416dc251d7714. The inferred type before this commit was `Any`, which seems reasonable.