[stable/percona-xtradb-cluster] fix StatefulSet apiVersion for Kubernetes 1.16+

[ustuzhanin]

• fixes [percona-xtradb-cluster] Kubernetes v1.16 compatibilty #21538

[k8s-ci-robot]

Hi @ustuzhanin. Thanks for your PR.

I'm waiting for a helm member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Any further update will cause the issue/pull request to no longer be considered stale. Thank you for your contributions.

[maver1ck]

/ok-to-test

[maver1ck]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: maver1ck, ustuzhanin

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