chore(deps): raise databricks-sql-connector upper bound to <4.3.1 to support 4.3.0

[sd-db]

Summary

Raises the databricks-sql-connector[pyarrow] upper bound from <4.2.7 to <4.3.1 and bumps the lock to 4.3.0 (released 2026-06-12 — the latest good release; 4.2.7 was yanked upstream, which is why the ceiling was previously <4.2.7).

No-code-change bump:

• 4.3.0's only additions are an opt-in Rust use_kernel backend and a thrift-0.23.0 revert; the default Thrift backend is unchanged.
• The new [kernel] extra is not pulled in by [pyarrow], and the connector API dbt uses (Connection, Cursor, __version__, exc.Error) is unchanged.
• requirements.lowest-direct.txt is left untouched — only the ceiling moved; the floor (>=4.1.1) is unchanged.

Testing

• Unit suite against 4.3.0: 1191 passed, 6 skipped
• Functional smoke on a SQL warehouse (databricks_uc_sql_endpoint): connection validation + table materialization + all column types — 4 passed

[github-actions]

Coverage report

This PR does not seem to contain any modification to coverable code.

[sd-db]

/integration-test

[github-actions]

Integration tests dispatched for PR #1518 by @sd-db. Track progress in the Actions tab.

[github-actions]

Integration results for PR #1518 — UC cluster ✅ success · SQL warehouse ✅ success · All-purpose cluster ✅ success · Shard coverage ✅ success

Run details.