br/streamhelper: fix subscribe error

[YuJuncen]

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:

• 3pointer
• joccau

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[joccau]

LGTM

[YuJuncen]

/merge

[ti-chi-bot]

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

Commit hash: 53af820

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #39745.

[sre-bot]

TiDB MergeCI notify

🔴 Bad News! New failing [1] after this pr merged.
These new failed integration tests seem to be caused by the current PR, please try to fix these new failed integration tests, thanks!

CI Name	Result	Duration	Compare with Parent commit
idc-jenkins-ci-tidb/integration-ddl-test	🟥 failed 1, success 5, total 6	5 min 10 sec	New failing
idc-jenkins-ci-tidb/mybatis-test	🔴 failed 1, success 0, total 1	4 min 16 sec	Existing failure
idc-jenkins-ci/integration-cdc-test	🟢 all 40 tests passed	19 min	Existing passed
idc-jenkins-ci-tidb/common-test	🟢 all 11 tests passed	16 min	Existing passed
idc-jenkins-ci-tidb/integration-common-test	🟢 all 17 tests passed	15 min	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-2	🟢 all 28 tests passed	6 min 29 sec	Existing passed
idc-jenkins-ci-tidb/sqllogic-test-1	🟢 all 26 tests passed	6 min 9 sec	Existing passed
idc-jenkins-ci-tidb/tics-test	🟢 all 1 tests passed	5 min 32 sec	Existing passed
idc-jenkins-ci-tidb/integration-compatibility-test	🟢 all 1 tests passed	3 min 27 sec	Existing passed
idc-jenkins-ci-tidb/plugin-test	🟢 build success, plugin test success	4min	Existing passed