fix: correct Milvus sparse vector search parameter from drop_ratio_build to drop_ratio_search

[ItsRoy69]

Summary

This PR fixes the incorrect parameter name used in Milvus sparse vector search operations.

Closes #5171

Type of change

• [x] Bug fix
• [ ] New feature
• [x] Breaking change
• [x] Improvement
• [ ] Model update
• [ ] Other:

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Checklist

• [x] Code complies with style guidelines
• [ ] Ran format/validation scripts (./scripts/format.sh and ./scripts/validate.sh)
• [x] Self-review completed
• [ ] Documentation updated (comments, docstrings)
• [ ] Examples and guides: Relevant cookbook examples have been included or updated (if applicable)
• [ ] Tested in clean environment
• [ ] Tests added/updated (if applicable)

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Additional Notes

Add any important context (deployment instructions, screenshots, security considerations, etc.)