We fail to do TypedDict tagged-union narrowing on this example:

from typing import TypedDict, Literal

class Ok(TypedDict):
   result: Literal["ok"]
   payload: bytes

class Err(TypedDict):
   result: Literal["error"]
   message: str

type Response = Ok | Err

def read(res: Response) -> bytes:
   if res["result"] == "ok":
        return res["payload"]
   else:
       raise Exception(res["message"])

But we do narrow if res: Ok | Err, or if Response = Ok | Err (legacy type alias instead of PEP 695 type alias).

We aren't handling a PEP 695 type alias as a union in narrowing. We should fix this, and also look for other cases in narrowing where we special-case unions, and ensure a PEP 695 alias to a union is handled the same way.