Fix positional GROUP BY in expect_column_values_to_have_consistent_casing

[sdebruyn]

Summary

• Replaces GROUP BY 1 with GROUP BY lower(distinct_values) in the expect_column_values_to_have_consistent_casing test macro
• T-SQL (Microsoft Fabric, SQL Server, Azure SQL) does not support positional GROUP BY references
• Explicit column expressions work on all SQL dialects

Fixes #44

Test plan

• Run expect_column_values_to_have_consistent_casing with display_inconsistent_columns=True on a T-SQL adapter — should no longer error
• Run the same test on PostgreSQL/Snowflake/BigQuery — should still pass
• Test both display_inconsistent_columns=True and display_inconsistent_columns=False paths

[Copilot]

Pull request overview

This PR fixes a cross-dialect compatibility issue in the expect_column_values_to_have_consistent_casing schema test by removing positional GROUP BY usage, which fails on T-SQL adapters (SQL Server / Azure SQL / Fabric).

Changes:

• Replaces GROUP BY 1 with an explicit GROUP BY lower(distinct_values) in the display_inconsistent_columns=True query path.

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