fix side effects baseline test flakiness due to corner case

PiperOrigin-RevId: 463419361

side_effects_penalties/side_effects_penalty_test.py

@@ -67,6 +67,8 @@ class BaselineTestCase(SideEffectsTestCase):
       }
       self.assertEqual(baseline_state, comparison_dict[key])
       current_state = next_state
+      if timestep.last():
+        return
 
 
 class StartBaselineTest(BaselineTestCase):