Update ml-agents/mlagents/trainers/tests/torch/saver/test_saver_reward_providers.py

Co-authored-by: Ruo-Ping (Rachel) Dong <ruoping.dong@unity3d.com>

ml-agents/mlagents/trainers/tests/torch/saver/test_saver_reward_providers.py

     saver = TorchSaver(trainer_settings, path1)
     saver.register(policy)
     saver.register(optimizer)
-    saver.initialize_or_load(policy)
+    saver.initialize_or_load()
     policy.set_step(2000)
     saver.save_checkpoint("MockBrain", 2000)