[Quality] Fix flaky test

ghstack-source-id: fa649fd
Pull-Request: #3211

Author: vmoens

test/test_env.py

@@ -3836,6 +3836,8 @@ def test_parallel(self, bwad, use_buffers, maybe_fork_ParallelEnv):
         finally:
             env.close(raise_if_closed=False)
             del env
+            time.sleep(0.1)
+            gc.collect()
 
     class AddString(Transform):
         def __init__(self):