Reverting back a typing change to fix the nightly which runs on an ol…

…der version of python.

PiperOrigin-RevId: 639810147
Change-Id: If7c36785b97e96a9068873caf8327c986b1a7a7b

circuit_training/environment/environment.py

@@ -18,7 +18,7 @@
 import math
 import os
 import time
-from typing import Any, Callable, Protocol
+from typing import Any, Callable, Optional, Protocol
 
 from absl import logging
 from circuit_training.dreamplace import dreamplace_core
@@ -151,7 +151,7 @@ def __init__(
       output_plc_file: str = '',
       cd_finetune: bool = False,
       cd_plc_file: str = 'ppo_cd_placement.plc',
-      train_step: tf.Variable | None = None,
+      train_step: Optional[tf.Variable] = None,
       output_all_features: bool = False,
       node_order: str = 'descending_size_macro_first',
       save_snapshot: bool = True,