Union type incorrectly satisfies TypeVar bound to Protocol with Self in contravariant position

[DanShaders]

Describe the bug

When a TypeVar is bound to a Protocol that uses Self as a parameter type (contravariant position), pyright incorrectly accepts a union type as satisfying the bound.

Code or Screenshots

from typing import Protocol, Self, final


class SelfSerializable(Protocol):
    @classmethod
    def serialize(cls, value: Self) -> bytes: ...


@final
class Foo:
    def __init__(self, x: int) -> None:
        self.x = x

    @classmethod
    def serialize(cls, value: Self) -> bytes:
        return value.x.to_bytes(4)


@final
class Bar:
    def __init__(self, name: str) -> None:
        self.name = name

    @classmethod
    def serialize(cls, value: Self) -> bytes:
        return value.name.encode()


def serialize_other[T: SelfSerializable](template: T, value: T) -> bytes:
    return type(template).serialize(value)


_ = serialize_other(Bar("name"), Foo(42))

0 diagnostics, runtime crash.

Writing def serialize[T](cls: type[T], value: T) -> bytes: ... in SelfSerializable makes no difference.

VS Code extension or command-line

1.1.408, through cmdline.