test: work around goroutine leak

[fzhedu]

What problem does this PR solve?

Issue Number: close #xxx

avoid goroutine leak from https://internal.pingcap.net/idc-jenkins/blue/rest/organizations/jenkins/pipelines/tidb_ghpr_unit_test/runs/67445/nodes/100/steps/319/log/?start=0
Problem Summary:

What is changed and how it works?

Proposal: xxx

What's Changed: work around this leak, fix this later with @hanfei1991 .

How it Works:

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• Need to cherry-pick to the release branch

Check List

Tests

Release note

• No release note

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• lzmhhh123
• winoros

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[fzhedu]

/merge

[ti-chi-bot]

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

Commit hash: 639de1e

[fzhedu]

/run-integration-copr-test

[hanfei1991]

/LGTM

[fzhedu]

/run-sqllogic-test-2

[ti-chi-bot]

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