Update k8s.gcr.io to registry.k8s.io (backport #1256)

[mergify]

This is an automatic backport of pull request #1256 done by Mergify.
Cherry-pick of b22ed68 has failed:

On branch mergify/bp/v1.3.x/pr-1256
Your branch is up to date with 'origin/v1.3.x'.

You are currently cherry-picking commit b22ed687.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   docs/content/manual/release-specific/v1.2.3/test-scalability-with-backing-image.md
	modified:   docs/content/manual/release-specific/v1.3.0/test-longhorn-manager-starting-scalability.md

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   mirror_csi_images/scripts/publish.sh

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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