Support lists in retry_on for RetryPolicy

Previously, `retry_on` in `RetryPolicy` accepted only exception classes, tuples of exception classes, or callables.
Update the `retry_on` type annotation to include `List[Type[Exception]]`

Changes:
- Updated `retry_on` in `RetryPolicy` to accept `List[Type[Exception]]`.

libs/langgraph/langgraph/pregel/types.py

@@ -1,5 +1,5 @@
 from collections import deque
-from typing import Any, Callable, Literal, NamedTuple, Optional, Type, Union
+from typing import Any, Callable, Literal, NamedTuple, Optional, Type, Union, List
 
 from langchain_core.runnables import Runnable, RunnableConfig
 
@@ -52,7 +52,7 @@ class RetryPolicy(NamedTuple):
     jitter: bool = True
     """Whether to add random jitter to the interval between retries."""
     retry_on: Union[
-        Type[Exception], tuple[Type[Exception], ...], Callable[[Exception], bool]
+        Type[Exception], List[Type[Exception]], tuple[Type[Exception], ...], Callable[[Exception], bool]
     ] = default_retry_on
     """List of exception classes that should trigger a retry, or a callable that returns True for exceptions that should trigger a retry."""