Pyrefly doesn't narrow if you save the result of an `isinstance` check to a local variable

[rchen152]

Describe the Bug

Example:

from typing import reveal_type

def f(x: int | str):
    isint = isinstance(x, int)
    if isint:
        # should be `int` but is instead `int | str`
        reveal_type(x)

Sandbox Link

https://pyrefly.org/sandbox/?project=N4IgZglgNgpgziAXKOBDAdgEwEYHsAeAdAA4CeS4ATrgLYAEALqcROgOZ0Q3G6UN2UYANxiooAfSbEYAHXRzMMMHTAAKfIk7p%2BAHzpwGlAJSI5dc5zit%2BAXkusDGAMYx1AGi0MjZixGUQrbVN0C1CBYVEJKVd8IxA3EABXBmg4EnJEEABiOgBVFKgIJhVE9CcU3HQ4OQUlFV4aVAZxdESabBhKdU1rIzoAWgA%2BfUNg0MEGRMoQsBkQADk2jspNYHwAXzm5eJAyQTAoUkIGWigKHIAFUn3D-QwcAjonSsg2KaaISsI5HIBlGBgdAAFgwGMQ4IgAPSQvZKQ6EXhsSEwdCQzC4JxwSHPdCvd4VVH1Sh0VBCVDQVDYWBPF4QN6UD6VOi4YgEtJyMgMIGVfoiShWJl2OYAZkIAEYAExbdAgdYJVDlCAiABi0BgFDQWDwRDIsqAA

(Only applicable for extension issues) IDE Information

No response