fix the table schema for cluster_tidb_index_usage (#18783)

[ti-chi-bot]

This is an automated cherry-pick of #18783

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What is changed, added or deleted? (Required)

Previously, the table schema for cluster_tidb_index_usage is wrong 🤦 . It's caused by a careless copy-paste. Now it's modified to the correct table schema.

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

• This PR is translated from: fix the table schema for cluster_tidb_index_usage docs-cn#18525
• 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

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