br: fix flaky test TestStoreRemoved

[YuJuncen]

What problem does this PR solve?

Issue Number: close #52791, close #52792

Problem Summary:
When dropping a subscription manager, the pending events will be dropped. So the test case will fail.

What changed and how does it work?

Wait until it seems there isn't new events.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

> go test --count=100 -run '^TestSomeOfStoreUnsupported|TestStoreRemoved$' github.com/pingcap/tidb/br/pkg/streamhelper
ok      github.com/pingcap/tidb/br/pkg/streamhelper     40.463s

• 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

[tiprow]

Hi @YuJuncen. Thanks for your PR.

PRs from untrusted users cannot be marked as trusted with /ok-to-test in this repo meaning untrusted PR authors can never trigger tests themselves. Collaborators can still trigger tests on the PR using /test all.

I understand the commands that are listed here.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[codecov]

Codecov Report

Merging #52834 (524355f) into master (65d4aea) will increase coverage by 2.6707%.
Report is 3 commits behind head on master.
The diff coverage is n/a.

Additional details and impacted files

@@               Coverage Diff                @@
##             master     #52834        +/-   ##
================================================
+ Coverage   72.3680%   75.0387%   +2.6707%     
================================================
  Files          1474       1477         +3     
  Lines        427589     430532      +2943     
================================================
+ Hits         309438     323066     +13628     
+ Misses        98921      87187     -11734     
- Partials      19230      20279      +1049     

Flag	Coverage Δ
integration	50.3543% <ø> (?)
unit	71.1879% <ø> (-0.0722%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	53.9957% <ø> (ø)
parser	∅ <ø> (∅)
br	61.0829% <ø> (+19.8736%)	⬆️

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• br/OWNERS [Leavrth]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-04-23 06:05:45.624680035 +0000 UTC m=+67502.364582940: ☑️ agreed by Leavrth.
• 2024-04-23 06:31:02.951753746 +0000 UTC m=+69019.691656658: ☑️ agreed by hawkingrei.

[tiprow]

@YuJuncen: 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
fast_test_tiprow	36e67e9	link	true	/test fast_test_tiprow

Full PR test history. Your PR dashboard.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository. I understand the commands that are listed here.

[YuJuncen]

/run-cherry-picker

[YuJuncen]

/run-cherry-picker

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #54572.