Manager: fix unit test

rFcfb17b178da2055ef12b2aa2ad8f7f778a952bc3 changed the semantics of
`SocketIOWorkerUpdate`, in the sense that any update that doesn't change
the worker status can omit `previous_status`. This commit adjusts the
unit test for this.

internal/manager/api_impl/worker_mgt_test.go

@@ -143,7 +143,6 @@ func TestRequestWorkerStatusChange(t *testing.T) {
 	mf.broadcaster.EXPECT().BroadcastWorkerUpdate(api.SocketIOWorkerUpdate{
 		Id:                worker.UUID,
 		Nickname:          worker.Name,
-		PreviousStatus:    &prevStatus,
 		Status:            prevStatus,
 		StatusRequested:   &requestStatus,
 		LazyStatusRequest: ptr(true),