test: fix multi_source test

[wk989898]

What problem does this PR solve?

Issue Number: ref #1068 ref pingcap/tiflow#12085

What is changed and how it works?

Check List

Tests

• Unit test
• Integration test

Questions

Will it cause performance regression or break compatibility?

Do you need to update user documentation, design documentation or monitoring documentation?

Release note

`None`.

[ti-chi-bot]

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hongyunyan

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-03-07 08:36:30.440167946 +0000 UTC m=+603503.569087689: ☑️ agreed by hongyunyan.

[wk989898]

/retest

[wk989898]

/retest