test: use process instead of thread

Signed-off-by: Yicheng-Lu-llll <[email protected]>

flytekit/core/type_engine.py

@@ -13,7 +13,7 @@
 import textwrap
 import typing
 from abc import ABC, abstractmethod
-from concurrent.futures import ThreadPoolExecutor
+from concurrent.futures import ProcessPoolExecutor
 from functools import lru_cache
 from typing import Dict, NamedTuple, Optional, Type, cast