fix: avoid 3.10+ set syntax

Author: adhtruong

tests/test_recursive_models.py

@@ -1,14 +1,15 @@
 from __future__ import annotations
 
 from dataclasses import dataclass
+from typing import Optional
 
 from polyfactory.factories.dataclass_factory import DataclassFactory
 
 
 @dataclass
 class Node:
     a: int
-    child: Node | None
+    child: Optional[Node]  # noqa: UP007
 
 
 def test_recusive_model() -> None: