test flake: TestPGCoordinatorDual_Mainline

Seen here: https://github.com/coder/coder/actions/runs/7186818506/job/19573060532


```
    t.go:93: 2023-12-12 20:19:55.916 [erro]  coord1.pgcoord.querier: failed to enqueue node update  coordinator_id=2e4b0f96-2e38-432b-9d1e-4c29ade2ad58  peer_id=934d2720-4b1c-4b0d-af06-5fb6fc3659b2  error="context canceled"
         *** slogtest: log detected at level ERROR; TEST FAILURE ***
```