ci: fix benchmark regress

[Xuanwo]

This PR will fix benchmark regress

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Parts of this PR were drafted with assistance from Codex (with gpt-5.2) and fully reviewed and edited by me. I take full responsibility for all changes.

[github-actions]

PR Review

Summary: This PR migrates from the deprecated list_indices() to describe_indices() and improves the data structure from list to set for index name lookup.

Assessment: ✅ LGTM

The changes are correct and appropriate:

1. list_indices() is deprecated (see python/python/lance/dataset.py:636-650) and describe_indices() is the recommended replacement
2. Both methods return objects with a .name attribute, so the code remains functionally correct
3. The change from list comprehension to set comprehension ([...] → {...}) improves lookup efficiency for in checks from O(n) to O(1)

No issues identified.