Update batch size notation to be consistent

Summary: fix notation of batch_size in RC safety module

Reviewed By: rodrigodesalvobraz

Differential Revision: D54178304

fbshipit-source-id: 9b4eefdb25dd3ecb81d895b53206840915a18385

pearl/safety_modules/reward_constrained_safety_module.py

@@ -61,7 +61,7 @@ def __init__(
         self.lr_lambda = lr_lambda
         self.lambda_constraint_ub_value = lambda_constraint_ub_value
         self.lambda_constraint = lambda_constraint_init_value
-        self.batch_size = batch_size
+        self._batch_size = batch_size
 
         # initialize parameters of cost critic
         assert hasattr(action_space, "action_dim")