test: optimize the test for TopN in index lookup pushdown.

[lcwangchao]

What problem does this PR solve?

Issue Number: close #64866

What changed and how does it work?

Add some tests for issue #64866 . However this bug is introduced by TiKV, we should wait TiKV to fix this issue

Check List

Tests

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

  • I checked and no code files have been changed.

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

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.6981%. Comparing base (00d697f) to head (04ec4b7).
⚠️ Report is 13 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #64867        +/-   ##
================================================
- Coverage   74.6711%   73.6981%   -0.9731%     
================================================
  Files          1891       1870        -21     
  Lines        515863     509535      -6328     
================================================
- Hits         385201     375518      -9683     
- Misses       106806     111909      +5103     
+ Partials      23856      22108      -1748     

Flag	Coverage Δ
integration	41.8836% <ø> (-6.2800%)	⬇️
unit	72.8876% <ø> (+0.6313%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	52.8700% <ø> (ø)
parser	∅ <ø> (∅)
br	46.4611% <ø> (-16.2099%)	⬇️

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[lcwangchao]

/retest

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: cfzjywxk, you06

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

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Details

Needs approval from an approver in each of these files:

• OWNERS [cfzjywxk,you06]

Approvers can indicate their approval by writing /approve in a comment
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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-12-08 06:47:34.600607921 +0000 UTC m=+850799.414385483: ☑️ agreed by cfzjywxk.
• 2025-12-08 06:49:17.347827072 +0000 UTC m=+850902.161604634: ☑️ agreed by you06.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.5: #64907.
But this PR has conflicts, please resolve them!