Fix regression

pettingzoo/test/parallel_test.py

@@ -114,7 +114,8 @@ def parallel_api_test(par_env: ParallelEnv, num_cycles=1000):
                     agent
                 ), "action_space should return the exact same space object (not a copy) for an agent (ensures that action space seeding works as expected). Consider decorating your action_space(self, agent) method with @functools.lru_cache(maxsize=None)"
 
-            for agent in live_agents:
+            # we make a copy of live_agents because live_agents changes during iteration
+            for agent in set(live_agents):
                 if terminated[agent] or truncated[agent]:
                     live_agents.remove(agent)