Don't restrict datetime instances

Author: dandavison

temporalio/worker/workflow_sandbox/_restrictions.py

@@ -17,6 +17,7 @@
 import warnings
 from copy import copy, deepcopy
 from dataclasses import dataclass
+from datetime import datetime
 from typing import (
     Any,
     Callable,
@@ -946,7 +947,7 @@ def r_op(obj: Any, other: Any) -> Any:
 
 def _is_restrictable(v: Any) -> bool:
     return v is not None and not isinstance(
-        v, (bool, int, float, complex, str, bytes, bytearray)
+        v, (bool, int, float, complex, str, bytes, bytearray, datetime)
     )