Fix get_object_vars() return type

[Triplkrypl]

I found in crash way, that get_object_vars can return array with int key.

https://onlinephp.io/c/9a628

[staabm]

Can numeric keys only occur for objects without a class?

If so it might make sense to use a return type extension instead which can narrow the type depending on the context.

edit: and I think you should target PHPStan 2.1.x