Accidental UT errors

[Poor12]

link: https://github.com/kubewharf/kubeadmiral/actions/runs/6307418487/job/17124013179?pr=226

The error case is t.Run("ClusterEventHandlers should receive correct old and new clusters", func(t *testing.T).
I ran it locally multiple times and found no similar errors.

I feel that there is a small time difference between the function entering assertionCh and calling callback, which is captured by the test case. I think it would be better to put the callBackCount.Add(1) before the assertionCh operation.

[Poor12]

/cc @limhawjia