cdc: integrated test "stop_downstream" is not stable

[zeminzhou]

Bug Report

1. Describe the bug

2. Minimal reproduce step (Required)

Send a PR.

3. What did you see instead (Required)

CI Integrated test pass.

4. What did you expect to see? (Required)

CI Integrated test failed.

5. What is your migration tool and TiKV version? (Required)

• TiKV:
• TiKV CDC: master
• TiKV BR:
• TiKV Online Bulk Load:

[github-actions]

This issue is stale because it has been open 30 days with no activity.