external: improve S3 error message (#59327)

[ti-chi-bot]

This is an automated cherry-pick of #59327

What problem does this PR solve?

Issue Number: close #59326

Problem Summary:

What changed and how does it work?

simply use %s instead of %v when printf

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

[Benjamin2037]

LGTM

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Benjamin2037, GMHDBJD

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• br/pkg/storage/OWNERS [Benjamin2037,GMHDBJD]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-06-30 12:50:14.057350994 +0000 UTC m=+1312866.780529976: ☑️ agreed by GMHDBJD.
• 2025-07-01 01:14:04.534450636 +0000 UTC m=+1357497.257629618: ☑️ agreed by Benjamin2037.

[GMHDBJD]

/retest

[codecov]

Codecov Report

Attention: Patch coverage is 46.66667% with 8 lines in your changes missing coverage. Please review.

Please upload report for BASE (release-8.1@61d7f3c). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.1     #62062   +/-   ##
================================================
  Coverage               ?   71.2423%           
================================================
  Files                  ?       1469           
  Lines                  ?     424871           
  Branches               ?          0           
================================================
  Hits                   ?     302688           
  Misses                 ?     101636           
  Partials               ?      20547           

Flag	Coverage Δ
unit	71.2423% <46.6666%> (?)

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

Components	Coverage Δ
dumpling	52.9656% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	41.5040% <0.0000%> (?)

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