[rpc] call threadPool.waitWorkComplete after listenerThread.join() to fix (#35394)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/35394
As above
ghstack-source-id: 101592571
Test Plan: Existing CI, no longer flaky
Differential Revision: D20632405
fbshipit-source-id: fbfd81470b3361371109af341f0db3ef8b3a415b
