Backup: Fix excessive retry delays caused by context errors

[3pointer]

What problem does this PR solve?

Issue Number: ref ##53835

Problem Summary:
Find region peer will retry 5 minutes which break the integration test 30s exits.

What changed and how does it work?

if context is cancelled, find region logic should return immediately.

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

[ti-chi-bot]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[ti-chi-bot]

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[ti-chi-bot]

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[tiprow]

Hi @3pointer. Thanks for your PR.

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[ti-chi-bot]

@3pointer: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
idc-jenkins-ci-tidb/unit-test	1488675	link	true	/test unit-test

Full PR test history. Your PR dashboard.

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