adapt arxiv search to new response format

[20001LastOrder]

Description

It seems recently the arXiv search has been changed to return an extra title element for the search result itself, which causes one existing test to fail. This fix aligns the number of title elements and summary elements to ensure consistency.

Type of change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Maintenance
• New release

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