br: fix backoffer can't handle multierrs (#54084)

[ti-chi-bot]

This is an automated cherry-pick of #54084

What problem does this PR solve?

Issue Number: close #54053

Problem Summary:

Backoffer can't recognize multierrs, therefore it would stop retry for recursive retry calling

What changed and how does it work?

Enable backoffer to recognize the multierr, and it will only check the last err returned

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 ✅

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Additional details and impacted files

@@               Coverage Diff                @@
##             release-6.5     #54109   +/-   ##
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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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• OWNERS [Leavrth]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-09-03 08:12:39.15656189 +0000 UTC m=+345683.674614816: ☑️ agreed by BornChanger.
• 2024-09-03 08:16:58.966569876 +0000 UTC m=+345943.484622800: ☑️ agreed by Leavrth.

[Leavrth]

/retest