Automatic merge from submit-queue
fix pdb validation bug on spec
**What this PR does / why we need it**:
When working on issue #48691, I found a bug on current [pdb validation on spec](https://github.com/kubernetes/kubernetes/blob/master/pkg/apis/policy/validation/validation.go#L41-L42). This validation is to check `PodDisruptionBudgetSpec` instead of the whole obj. Currently when doing updates, this check will fail as always.
**Which issue this PR fixes** : fix#48691
**Special notes for your reviewer**:
**Release note**:
```release-note
fix pdb validation bug on PodDisruptionBudgetSpec
```