Literal["..."]s incorrectly assignable to protocol with __getitem__(slice) -> Self #20058

from typing import Protocol, Self, Literal

class Slicable(Protocol):
    def __getitem__(self, arg: slice, /) -> Self:
        ...

class Parser[X: Slicable]:
    def handle(self, input: X) -> tuple[X, X]:
        return input[:2], input[2:]

parser = Parser[Literal["banana"]]()
#^ no error, but expected: Literal['banana'] does not satisfy Slicable bound

left, right = parser.handle("banana")
reveal_type(left)  # revealed as: Literal['banana'], but 'ba' at runtime
reveal_type(right) # revealed as: Literal['banana'], but 'nana' at runtime