[CI] StickyWorkflowDrainShutdownTest.testShutdown is flaky

[Quinn-With-Two-Ns]

In CI StickyWorkflowDrainShutdownTest.testShutdown is flaky. Looking at it I think there is a race condition in worker shutdown if no activities are registered.

https://github.com/temporalio/sdk-java/actions/runs/8667250325/job/23771031368?pr=2021