[Ut] Fix be ut failed for topn_function_test

[caiconghui]

Proposed changes

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Types of changes

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• [] Bugfix (non-breaking change which fixes an issue)
• [] New feature (non-breaking change which adds functionality)
• [] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [] Documentation Update (if none of the other choices apply)
• [] Code refactor (Modify the code structure, format the code, etc...)

Checklist

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• [] I have created an issue on (Fix [Ut] run topn_function_test failed in be unit test #5450) and described the bug/feature there in detail
• [] Compiling and unit tests pass locally with my changes
• [] I have added tests that prove my fix is effective or that my feature works
• [] If these changes need document changes, I have updated the document
• [] Any dependent changes have been merged

Further comments

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[kangkaisen]

+1