Pyrefly should promote literals when inferring tuple types for attributes #1494

class A:
    def __init__(self):
        self.x = (42, 42)
    def f(self):
        self.x = (0, 0)  # error: `tuple[Literal[0], Literal[0]]` is not assignable to attribute `x` with type `tuple[Literal[42], Literal[42]]`