[duckdb-labs bot] Bump DuckDB submodule (#412)

Bump duckdb submodule:
- Target branch: v1.5-variegata
- Date: 2026-04-04 05:50:14
- DuckDB SHA: cbc6f2230e53b51aa632b117a9722afa42f2a04f
- Trigger:
https://github.com/duckdb/duckdb-python/actions/runs/23972233498

Author: evertlammerts