docs: remove duplicate 'of' in REC certificates docs

[mrchatam]

Summary

Fix duplicated preposition in Redis Enterprise on Kubernetes certificate docs: "list of of certificates" → "list of certificates".

Test plan

• Confirmed the sentence reads correctly in each versioned copy updated
• No other wording changes

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Note

Low Risk
Documentation-only copy edit with no impact on product code, configuration, or security behavior.

Overview
Fixes a wording typo in the Manage REC certificates intro across five Kubernetes doc versions (7.4.6, 7.8.4, 7.8.6, 7.22, and 8.0): "list of of certificates" is corrected to "list of certificates" in the sentence that links to the certificates table. No other content or behavior changes.

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[mrchatam]

Closing: Redis CLA is not signed for this account, so these docs PRs cannot proceed. Will reopen after CLA is signed if still needed.