Describe the Bug

When we assign instance attributes, we need to check for unbound type variables, but the check is incorrectly also flagging type variables which are bound by the right-hand side expression.

from typing import reveal_type

def f[T](x: T) -> T:
    return x

class C:
    def m[U](self, x: U) -> U:
        return x

class D:
    def __init__(self, c: C):
        self.f = f # Unexpected invalid-type-var
        self.g = c.m # Unexpected invalid-type-var

def test(o: D):
    reveal_type(o.f) # should be [T](x: T) -> T
    reveal_type(o.g) # should be BoundMethod[C, [U](self: C, x: U) -> U]

I believe the error is happening here:

We collect the quantified types from the RHS expression, but we only want unbound quantifieds.

Sandbox Link

https://pyrefly.org/sandbox/?project=N4IgZglgNgpgziAXKOBDAdgEwEYHsAeAdAA4CeS4ATrgLYAEALqcROgOZ0Q3G6UN2UYANxiooAfSbEYAHXRzMMMHTABtACoBdABT5EddQEo6AWgB8BxHLo2BMBgFdK6OvjlyAxlFRw4dAMJWLraKyjSqAKo6cDBQYAA0rvoRxuZ0EUG2WXaOzq7u6F4%2BfgAimSFKdOLirBAM1doxcYke%2Bv6G5dl0TWCEygC8KtZd3bG9HIMehDQFoYzwDNq4%2BiUdwzaCImKSzDBLfcYAxN0AFrgOUJh02DB0Gjp6BqkW6ut2WxJSe7iEbEen50u11uACFzlgALL2M6YVT%2BRKRaJjNqJR4pUwWKIgeIgMiCMBQUiEBi0KAUY4ABVI%2BMJ3QwOAIdA8uHQkDYTlQDAgLMIcmOAGUYLcTgwGMQ4IgAPSSvFKQmEXhsSUwdCSzC4DxwSXM1kQdmUTnc1UqXh0VBCVDQVDYWBMllsjlcll0XDEJ3oOC89BkBhndAmESUOBGuiDGQgADMhAAjAAmcNyEAAXxxqA8XJEADFoDAKGgsHgiGRk0A

(Only applicable for extension issues) IDE Information

No response