Update trajectory_writer_test, so that it works fine for async server.
Update trajectory_writer_test, so that it works fine for async server.

PiperOrigin-RevId: 388422726
Change-Id: Ifaf86192e588c8ee18eaa05273d8ee7d6e0fce4b

deepmind/reverb,deepmind/reverb,deepmind/reverb,deepmind/reverb