add a note on max_prepared_stmt_count for 6.5.2

[ran-huang]

What is changed, added or deleted? (Required)

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For details, see tips for choosing the affected versions.

• master (the latest development version)
• v7.1 (TiDB 7.1 versions)
• v7.0 (TiDB 7.0 versions)
• v6.6 (TiDB 6.6 versions)
• v6.5 (TiDB 6.5 versions)
• 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)

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

• This PR is translated from:add a note on max_prepared_stmt_count for 6.5.2 docs-cn#13819
• 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]

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• qiancai

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[ran-huang]

/merge

[ti-chi-bot]

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

Commit hash: b67cd56

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.5: #13372.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.6: #13373.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.0: #13374.