Fix description about hot-region-cache-hits-threshold

[Joyinqin]

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

What is changed, added or deleted? (Required)

Fix description about hot-region-cache-hits-threshold.

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

• master (the latest development version)
• v5.1 (TiDB 5.1 versions)
• v5.0 (TiDB 5.0 versions)
• v4.0 (TiDB 4.0 versions)
• 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: Fix description about hot-region-cache-hits-threshold docs-cn#6339
• 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

[Joyinqin]

/label needs-cherry-pick-release-5.0
/label needs-cherry-pick-release-4.0
/translation from-docs

[ti-chi-bot]

@Joyinqin: The label(s) translation/from-docs cannot be applied, because the repository doesn't have them.

In response to this:

/label needs-cherry-pick-release-5.0
/label needs-cherry-pick-release-4.0
/translation from-docs

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[Joyinqin]

/translation from-docs-cn

[TomShawn]

/lgtm
/label require-LGT1

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• TomShawn

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[TomShawn]

/merge

[ti-chi-bot]

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

Commit hash: da403b1

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #5722.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #5723.