Automatic merge from submit-queue (batch tested with PRs 51180, 51893)
Clear alpha MountPropagation fields.
This is leftover from #50924, mount propagation introduced a new field that needs to be cleared.
**Which issue this PR fixes**
fixes#51738
**Release note**:
```release-note
NONE
```
@k8s-mirror-api-machinery-pr-reviews
/assign @liggitt