Bump dbt-sql to DBR 16.4 LTS for classic compute

[rugpanov]

Changes

Follow-up from #6378: bump the dbt-sql bundle template's classic (non-serverless) compute to Databricks Runtime 16.4 LTS.

• dbt-sql: bump latest_lts_dbr_version from 15.4.x-scala2.12 to 16.4.x-scala2.12. This matches the default template (already pinned to 16.4) and aligns the cluster runtime's Python version (3.12) with serverless environment version 5.
• dbt-sql: remove the unused, TODO-flagged latest_lts_db_connect_version_spec macro (flagged for removal in Bump default serverless environment version to 5 #6378; no template references it).

The unrelated dead-code removal in default-sql/library/versions.tmpl has been split into a separate PR.

Tests

• New acceptance variant acceptance/bundle/templates/dbt-sql-classic initializes dbt-sql with serverless: no and diffs the generated job against the serverless golden, locking in the classic new_cluster spark_version: 16.4.x-scala2.12. Before this, no acceptance test rendered the classic (non-serverless) path.
• Note for future editors: this variant diffs against the sibling dbt-sql test's committed golden, so any change to the base dbt-sql job template requires regenerating both goldens.
• Existing dbt-sql (serverless) and default-sql template goldens are unchanged; acceptance tests pass.

This pull request and its description were written by Isaac.

[eng-dev-ecosystem-bot]

Integration test report

Commit: 16953f4

Run: 33157663368

	Env	💚​RECOVERED	🙈​SKIP	✅​pass	🙈​skip	Time
💚​	aws linux	1	1	274	1195	4:02
💚​	aws windows	1	1	276	1193	3:34
💚​	azure linux	1	1	273	1195	4:03
💚​	azure windows	1	1	275	1193	3:34
💚​	gcp linux	1	1	274	1195	4:25
💚​	gcp windows	1	1	276	1193	4:32

	Test Name	aws linux	aws windows	azure linux	azure windows	gcp linux	gcp windows
💚​	TestAccept	💚​R	💚​R	💚​R	💚​R	💚​R	💚​R
🙈​	TestAccept/ssh/connection	🙈​S	🙈​S	🙈​S	🙈​S	🙈​S	🙈​S

Top 3 slowest tests (at least 2 minutes):

duration	env	testname
4:29	gcp windows	TestAccept
3:30	aws windows	TestAccept
3:30	azure windows	TestAccept

[github-actions]

Approval status: pending

/acceptance/bundle/ - needs approval

4 files changed
Suggested: @denik
Also eligible: @janniklasrose, @andrewnester, @shreyas-goenka, @lennartkats-db, @anton-107, @pietern

/libs/template/ - needs approval

Files: libs/template/templates/dbt-sql/library/versions.tmpl
Suggested: @denik
Also eligible: @janniklasrose, @andrewnester, @shreyas-goenka, @lennartkats-db, @anton-107, @pietern

General files (require maintainer)

Files: .nextchanges/bundles/dbt-sql-classic-dbr-16-4.md
Based on git history:

• @denik -- recent work in .nextchanges/bundles/

_{Any maintainer (@andrewnester, @anton-107, @denik, @pietern, @shreyas-goenka, @simonfaltum, @renaudhartert-db, @janniklasrose, @lennartkats-db, @rclarey) can approve all areas.
See OWNERS for ownership rules.}