Intermittent test failure: Offline Entities: Timeout of 16000ms exceeded

[alxndrsn]

Seen at https://github.com/getodk/central-backend/actions/runs/28377183995/job/84069808050 (PR build, but unlikely to be caused by the PR's changes).

Previously exceeded 8000ms at #1813

  1) Offline Entities
       locking an entity while processing a related submission @slow
         should concurrently process an offline create + update:
     Error: Timeout of 16000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. (/home/runner/work/central-backend/central-backend/test/integration/api/offline-entities.js)
      at listOnTimeout (node:internal/timers:605:17)
      at process.processTimers (node:internal/timers:541:7)

[alxndrsn]

Seen again at https://github.com/getodk/central-backend/actions/runs/28703816381/job/85126179211:

[1](https://github.com/getodk/central-backend/actions/runs/28703816381/job/85126179211#step:9:22622)

  2515 passing (3m)
  5 pending
  1 failing

  1) Offline Entities
       locking an entity while processing a related submission @slow
         should concurrently process an offline create + update:
     Error: Timeout of 16000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. (/home/runner/work/central-backend/central-backend/test/integration/api/offline-entities.js)
      at listOnTimeout (node:internal/timers:605:17)
      at process.processTimers (node:internal/timers:541:7)