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Add UT for pkg/kubectl/autoscale_test.go

**What this PR does / why we need it**:

I find there is no UT for testing pkg/kubectl `HorizontalPodAutoscalerV1.generate(params)`. This PR add some UTs in pkg/kubectl/autoscale_test.go

**Which issue this PR fixes** : fixes #50810

**Special notes for your reviewer**:

**Release note**:

```release-note
NONE
```

/sig cli