br: add <Code>RequestTimeout</Code> to list of retryable errors

[kennytm]

What problem does this PR solve?

Issue Number: close #41756

Problem Summary:

Some S3-compatible external storage does not return an error response with a human-readable <Message> tag. BR relied on its content and thus failed to recognize a RequestTimeout error is in fact retryable.

What is changed and how it works?

Added the error code into the list of phrases to check.

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.

BR can now properly retry on RequestTimeout transient errors when backing up to Baidu Object Storage (BOS).

[ti-chi-bot]

[REVIEW NOTIFICATION]

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• fengou1
• joccau

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[kennytm]

Note that the customer facing this issue is still on release-5.1. Is it ok to cherry-pick this + #34930 altogether to v5.1.6?

[fengou1]

it looks good to me

[ti-chi-bot]

@tonyxuqqi: Thanks for your review. The bot only counts approvals from reviewers and higher roles in list, but you're still welcome to leave your comments.

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[joccau]

LGTM

[joccau]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 8253e21

[joccau]

/run-integration-br-test

[joccau]

/test unit-test

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.2: #42247.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.3: #42248.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.4: #42249.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.5: #42251.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.6: #42252.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-5.4: #42253.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.0: #42254.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.1: #42255.