Update wording in placement rules in sql

[TomShawn]

What is changed, added or deleted? (Required)

Update wording in placement rules in sql

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• master (the latest development version)
• v5.3 (TiDB 5.3 versions)
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• v5.1 (TiDB 5.1 versions)
• v5.0 (TiDB 5.0 versions)
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• v3.1 (TiDB 3.1 versions)
• v3.0 (TiDB 3.0 versions)
• v2.1 (TiDB 2.1 versions)

What is the related PR or file link(s)?

• This PR is translated from: placement rules: fix bad wording docs#6818
• 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:

• Liuxiaozhen12

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[TomShawn]

/remove-status LGT1
/status LGT2
This PR is also approved by @xhebox .

[TomShawn]

/merge

[ti-chi-bot]

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

Commit hash: ae39b13