cdc: flaky test: `Fail to get ts` from TiKV

[pingyu]

Bug Report

1. Describe the bug

Fail to get ts from TiKV.
See https://do.pingcap.net/jenkins/blue/organizations/jenkins/tikv%2Fmigration%2Fpull_integration_test/detail/pull_integration_test/56/pipeline/245

2. Minimal reproduce step (Required)

3. What did you see instead (Required)

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

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

• TiKV:
• TiKV CDC: fa2b180
• TiKV BR:
• TiKV Online Bulk Load:

[github-actions]

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