fix typos in docs

[qiancai]

First-time contributors' checklist

• [ ] I've signed Contributor License Agreement that's required for repo owners to accept my contribution.

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Which TiDB Operator version(s) do your changes apply to? (Required)

• [ ] master (the latest development version)
• [ ] v1.6 (TiDB Operator 1.6 versions)
• [ ] v1.5 (TiDB Operator 1.5 versions)
• [ ] v1.4 (TiDB Operator 1.4 versions)
• [ ] v1.3 (TiDB Operator 1.3 versions)
• [ ] v1.2 (TiDB Operator 1.2 versions)

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[ti-chi-bot[bot]]

[LGTM Timeline notifier]

Timeline:

• 2024-04-28 10:17:27.460530306 +0000 UTC m=+179601.217665879: :ballot_box_with_check: agreed by csuzhangxc.
• 2024-05-15 08:31:06.333202764 +0000 UTC m=+1642020.090338334: :ballot_box_with_check: agreed by Oreoxmt.

[qiancai]

/approve

[ti-chi-bot[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: qiancai

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[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-1.5: #2570.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-1.6: #2571.