fix typo in userguide_3.0.md

[zhangyangyu]

What problem does this PR solve?

What is changed and how it works?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Code changes

• Has exported function/method change
• Has exported variable/fields change
• Has interface methods change
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation
• Need to update the tidb-ansible repository
• Need to be included in the release note

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: shiyuhang0

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-01-17 02:37:40.144442694 +0000 UTC m=+323501.708740399: ☑️ agreed by shiyuhang0.