lightning: fix a wrong description in command line flags

[ran-huang]

What is changed, added or deleted? (Required)

as title.

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

Tips for choosing the affected version(s):

By default, CHOOSE MASTER ONLY so your changes will be applied to the next TiDB major or minor releases. If your PR involves a product feature behavior change or a compatibility change, CHOOSE THE AFFECTED RELEASE BRANCH(ES) AND MASTER.

For details, see tips for choosing the affected versions (in Chinese).

• [x] master (the latest development version)
• [ ] v6.3 (TiDB 6.3 versions)
• [x] v6.1 (TiDB 6.1 versions)
• [ ] v5.4 (TiDB 5.4 versions)
• [ ] v5.3 (TiDB 5.3 versions)
• [ ] v5.2 (TiDB 5.2 versions)
• [ ] v5.1 (TiDB 5.1 versions)
• [ ] v5.0 (TiDB 5.0 versions)

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• Other reference link(s):

Do your changes match any of the following descriptions?

• [ ] Delete files
• [ ] Change aliases
• [ ] Need modification after applied to another branch
• [ ] Might cause conflicts after applied to another branch

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• lilin90

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[ti-chi-bot]

@ran-huang: PR needs rebase.

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[qiancai]

Removed the needs-cherry-pick-release-6.4 label because the v6.4 docs have been archived at https://docs-archive.pingcap.com/zh/tidb/v6.4 and will no longer receive new updates.

[ran-huang]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: b5127725cd74333de8a0e5fec9045ad93962080c

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.6: #13734.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.0: #13735.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.1: #13736.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.5: #13737.