Automatic merge from submit-queue (batch tested with PRs 66665, 66707, 66596). 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>.
Update webhook test image to multi-arch
**What this PR does / why we need it**:
Use the `image-util.sh` to build the container image so we can generate the full manifest for multi-arch images
**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixes #
**Special notes for your reviewer**:
/cc @mkumatag
/cc @luxas
**Release note**:
```release-note
NONE
```
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