add the parent node to "__main__"

Not having a parent leads to weird situations, like `root()` returning
   the node itself, not a `Module`.

astroid/nodes/scoped_nodes/scoped_nodes.py

@@ -354,7 +354,9 @@ def getattr(
  if name in self.special_attributes and not ignore_locals and not name_in_locals:
  result = [self.special_attributes.lookup(name)]
  if name == "__name__":
- result.append(const_factory("__main__"))
+ main_const = const_factory("__main__")
+ main_const.parent = AstroidManager().builtins_module
+ result.append(main_const)
  elif not ignore_locals and name_in_locals:
  result = self.locals[name]
  elif self.package: