solve unsafe usage

[Chononut]

参数change是NodeChange类型，Nodechange是6个类型的联合类型。只有当6个类型同时拥有同一属性时，TS才能找到这一属性。6个类型只有NodePositionChange有dragging属性，在使用change.dragging之前需要使用条件语句类型收缩。

[gru-agent]

TestGru Assignment

Summary

Link	CommitId	Status	Reason
Detail	c4bec83	🚫 Skipped	No files need to be tested {"projects/app/src/pageComponents/app/detail/WorkflowComponents/Flow/hooks/useWorkflow.tsx":"File path does not match include patterns."}

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[c121914yu]

没看懂有啥区别，不是已经推断出来了么？