Binder fails to track loops correctly

[hauntsaninja]

# mypy: enable-error-code=redundant-expr
from __future__ import annotations

class Node:
 parent: Node | None
 is_valid: bool

 def traverse_needs_fixing(self) -> Node | None:
 it: Node | None
 it = self
 while it is not None and it.is_valid: # E: Left operand of "and" is always true [redundant-expr]
 it = it.parent
 return it

 def traverse(self) -> Node | None:
 # this only works because mypy does not narrow on initial assignment
 # which is something we'd like to change, see #2008
 it: Node | None = self
 while it is not None and it.is_valid:
 it = it.parent
 return it