Manager: increase wait time in worker timeout test

Instead of waiting for 1ns, wait for 1ms. That's more stable on my laptop,
and still short enough to not really slow down the test.

internal/manager/persistence/workers_test.go

@@ -408,7 +408,7 @@ func TestSummarizeWorkerStatusesTimeout(t *testing.T) {
 
 	// Force a timeout of the context. And yes, even when a nanosecond is quite
 	// short, it is still necessary to wait.
-	time.Sleep(2 * time.Nanosecond)
+	time.Sleep(1 * time.Millisecond)
 
 	// Test the summary.
 	summary, err := f.db.SummarizeWorkerStatuses(subCtx)