Automatic merge from submit-queue (batch tested with PRs 56639, 56746, 56715, 56673, 56726). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.
Fix a typo in kubectl/diff cmd long description.
**What this PR does / why we need it**:
Correct a typo in kubelet alpha diff cmd long description.
**Release note**:
```release-note
NONE
```
6541b1ae06