fix: load gets stuck probably (#29191) (#29192)

we found the load got stuck probably, and reviewed the logs.

the target observer seems not working, the reason is the taskDispatcher
removes the task in a goroutine, and modifies the task status after
committing the task into the goroutine pool, but this may happen after
the task removed, which leads to the task will never be removed

related #29086
pr: #29191

Signed-off-by: yah01 <yang.cen@zilliz.com>

internal/querycoordv2/observers/task_dispatcher.go

@@ -96,12 +96,12 @@ func (d *taskDispatcher[K]) schedule(ctx context.Context) {
 		case <-d.notifyCh:
 			d.tasks.Range(func(k K, submitted bool) bool {
 				if !submitted {
+					d.tasks.Insert(k, true)
 					d.pool.Submit(func() (any, error) {
 						d.taskRunner(ctx, k)
 						d.tasks.Remove(k)
 						return struct{}{}, nil
 					})
-					d.tasks.Insert(k, true)
 				}
 				return true
 			})