br/streamhelper: fix subscribe error (#39689)

[ti-chi-bot]

This is an automated cherry-pick of #39689

Signed-off-by: hillium [email protected]

What problem does this PR solve?

Issue Number: close #39688

Problem Summary:
We clear the subscription error before canceling the subscription, once there are some errors emitted during canceling, there would be a error-retry loop.

What is changed and how it works?

This PR:

• Make subscriptions don't emit error when meeting Status(codes.Canceled, _).
• Clear the error after canceling current subscription.

Check List

Tests

• Unit test

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

Fixed a bug that may cause TiDB send unexpected unnecessary requests to TiKV.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• Leavrth
• YuJuncen

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[hawkingrei]

/merge

[ti-chi-bot]

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

Commit hash: a8ea803

[ti-chi-bot]

@ti-chi-bot: Your PR was out of date, I have automatically updated it for you.

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[YuJuncen]

/merge