statistics: fix init topn not sorted (#34234)

[ti-srebot]

cherry-pick #34234 to release-6.0
You can switch your code base to this Pull Request by using git-extras:

# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/34316

After apply modifications, you can push your change to this PR via:

git push [email protected]:ti-srebot/tidb.git pr/34316:release-6.0-e1580175e700

---

What problem does this PR solve?

Issue Number: close #34216 ref #32758

Problem Summary: Please see the issue.

What is changed and how it works?

Check List

Tests

• Unit test
• Integration test
• Manual test (please see the comments below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has not been approved.

To complete the pull request process, please ask the reviewers in the list to review by filling /cc @reviewer in the comment.
After your PR has acquired the required number of LGTMs, you can assign this pull request to the committer in the list by filling /assign @committer in the comment to help you merge this pull request.

The full list of commands accepted by this bot can be found here.

Reviewer can indicate their review by submitting an approval review.
Reviewer can cancel approval by submitting a request changes review.

[ti-srebot]

/run-all-tests

[ti-srebot]

@time-and-fate you're already a collaborator in bot's repo.

[xhebox]

closed for DMR version