Update index secret for cluster-init collection

[psalajova]

Update the cluster-init____index secret in GSM after syncing the individual cluster-init secrets -- previously, individual cluster-init secrets were synced to GSM but the collection's index secret wasn't being updated.

Follow-up for: #4750

[openshift-ci]

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[openshift-ci]

@psalajova: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
ci/prow/images	391b441	link	true	/test images
ci/prow/breaking-changes	391b441	link	false	/test breaking-changes

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