fix: prevent duplicate alias in --empty mode for inline ref/source

[sd-db]

Summary

• Sets require_alias: bool = False on DatabricksRelation, preventing render_limited() from injecting a _dbt_limit_subq_* alias that conflicts with user-provided AS aliases when running dbt run --empty
• Adds conformance tests for --empty mode (BaseTestEmpty and BaseTestEmptyInlineSourceRef)
• Adds a unit test verifying render_limited() output has no trailing subquery alias

Context

When dbt run --empty is used, dbt wraps ref() and source() in a zero-row subquery. BaseRelation defaults to require_alias=True, which appends an auto-generated alias (_dbt_limit_subq_{table}). If the user also has an AS alias in their SQL (e.g. {{ ref('orders') }} AS orders), the two aliases conflict and produce invalid SQL.

Databricks SQL does not require subquery aliases, so require_alias should be False.

Resolves dbt-labs/dbt-adapters#660 for Databricks.

Test plan

• Unit test: test_render_limited_with_empty_no_alias — asserts render_limited() produces no trailing alias with limit=0
• Functional test: TestDatabricksEmptyInlineSourceRef — end-to-end against live cluster, dbt run --empty with inline source alias
• Functional test: TestDatabricksEmpty — general --empty conformance
• All 721 existing unit tests pass (0 regressions)

[github-actions]

Coverage report

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File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
dbt/adapters/databricks
relation.py
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