br: fix bug file-not-found error for gcs (#65058)

[ti-chi-bot]

This is an automated cherry-pick of #65058

What problem does this PR solve?

Issue Number: close #63567

Problem Summary: retry br log truncate, it may fail forever, only for gcs storage

What changed and how does it work?

deal with file-not-exist situation correctly as it has been deleted which should return no-error.

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.
⚠️ Please upload report for BASE (release-8.5@2675484). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.5     #65404   +/-   ##
================================================
  Coverage               ?   73.2526%           
================================================
  Files                  ?       1680           
  Lines                  ?     469212           
  Branches               ?          0           
================================================
  Hits                   ?     343710           
  Misses                 ?     102651           
  Partials               ?      22851           

Flag	Coverage Δ
integration	51.1459% <20.0000%> (?)
unit	64.9442% <100.0000%> (?)

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

Components	Coverage Δ
dumpling	52.9278% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	63.7044% <0.0000%> (?)

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[EmmaDuDu]

/retest

[EmmaDuDu]

/test unit-test

[tiprow]

@EmmaDuDu: The specified target(s) for /test were not found.
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/test unit-test

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[ti-chi-bot]

@YuJuncen: Your lgtm message is repeated, so it is ignored.

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: BornChanger, YuJuncen

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Details

Needs approval from an approver in each of these files:

• OWNERS [BornChanger,YuJuncen]
• br/pkg/storage/OWNERS [BornChanger,YuJuncen]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-01-06 07:22:09.393308787 +0000 UTC m=+686885.211617209: ☑️ agreed by YuJuncen.
• 2026-01-07 04:19:05.432994564 +0000 UTC m=+762301.251303016: ☑️ agreed by BornChanger.