Automatic merge from submit-queue (batch tested with PRs 55439, 58564, 59028, 59169, 59259). 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>.

Add unit test for pkg/serviceaccount.

**What this PR does / why we need it**:
Add Unit test for pkg/serviceaccount.

**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
None

**Special notes for your reviewer**:
None

**Release note**:

```release-note
NONE
```