br: fix go leak when nothing to restore

[Tristan1900]

What problem does this PR solve?

Issue Number: close #58624

Problem Summary:

What changed and how does it work?

recent change makes the ctx in GoSwitchToImportMode not inherit from the main ctx, thus when main ctx cancelled the go routine didn't return, and the manual cleanup logic wasn't called when nothing to return either, leading to a go routine leak found in int test

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

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[tiprow]

Hi @Tristan1900. Thanks for your PR.

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[Tristan1900]

it should go though to the end of method and get set anyway

[codecov]

Codecov Report

Attention: Patch coverage is 88.88889% with 1 line in your changes missing coverage. Please review.

Project coverage is 74.7942%. Comparing base (cdcc291) to head (a1f8182).
Report is 12 commits behind head on master.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #58626        +/-   ##
================================================
+ Coverage   73.5455%   74.7942%   +1.2487%     
================================================
  Files          1680       1695        +15     
  Lines        464730     466857      +2127     
================================================
+ Hits         341788     349182      +7394     
+ Misses       102118      96094      -6024     
- Partials      20824      21581       +757     

Flag	Coverage Δ
integration	46.0252% <77.7777%> (?)
unit	72.3298% <44.4444%> (+0.0360%)	⬆️

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

Components	Coverage Δ
dumpling	52.6910% <ø> (ø)
parser	∅ <ø> (∅)
br	61.5290% <88.8888%> (+15.7485%)	⬆️

[Tristan1900]

/assign @3pointer