br: improve TestNewImportSSTBackofferWithSucess

[hawkingrei]

What problem does this PR solve?

Issue Number: close #45684

Problem Summary:

What is changed and how it works?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps 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

[codecov]

Codecov Report

Merging #45683 (8164661) into master (9794ea5) will increase coverage by 0.0398%.
Report is 4 commits behind head on master.
The diff coverage is n/a.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #45683        +/-   ##
================================================
+ Coverage   73.2285%   73.2683%   +0.0397%     
================================================
  Files          1265       1268         +3     
  Lines        389826     390601       +775     
================================================
+ Hits         285464     286187       +723     
- Misses        86053      86093        +40     
- Partials      18309      18321        +12     

Flag	Coverage Δ
integration	78.1388% <ø> (?)
unit	73.2599% <ø> (+0.0313%)	⬆️

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

Components	Coverage Δ
dumpling	54.0444% <ø> (ø)
parser	85.0417% <ø> (ø)
br	52.1351% <ø> (+0.0441%)	⬆️

[D3Hunter]

@3pointer ptal

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: D3Hunter, Leavrth

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-07-31 07:02:42.043974502 +0000 UTC m=+82445.986323027: ☑️ agreed by D3Hunter.
• 2023-07-31 07:09:09.631507649 +0000 UTC m=+82833.573856412: ☑️ agreed by Leavrth.