fix: [10kcp] Fix concurrent scheule (#38974)

supplement to pr: https://github.com/milvus-io/milvus/pull/38566

Signed-off-by: bigsheeper <yihao.dai@zilliz.com>

internal/querycoordv2/task/scheduler.go

@@ -172,6 +172,7 @@ type taskScheduler struct {
 	cluster   session.Cluster
 	nodeMgr   *session.NodeManager
 
+	scheduleMu   sync.Mutex           // guards schedule()
 	collKeyLock  *lock.KeyLock[int64] // guards Add()
 	tasks        *ConcurrentMap[UniqueID, struct{}]
 	segmentTasks *ConcurrentMap[replicaSegmentIndex, Task]
@@ -502,6 +503,8 @@ func (scheduler *taskScheduler) Dispatch(node int64) {
 		log.Info("scheduler stopped")
 
 	default:
+		scheduler.scheduleMu.Lock()
+		defer scheduler.scheduleMu.Unlock()
 		scheduler.schedule(node)
 	}
 }