fix: convert workflow job spec to SDK dataclasses before jobs.create() (#1338)

[aarushisingh04]

resolves #1360

description

WorkflowJobApi.create() passes plain dicts to workspace_client.jobs.create(**converted_job_spec). the databricks sdk's jobs.create() iterates tasks calling v.as_dict() on each (confirmed via JobsAPI.create source inspection). plain dicts have no .as_dict() which caused the 'dict' object has no attribute 'as_dict' error.

1. the fix uses JobSettings.from_dict() + .as_shallow_dict() to convert the plain dict job spec into proper sdk dataclasses before calling jobs.create().
2. as_shallow_dict() is the correct choice here : it unpacks top-level fields as kwargs (matching the jobs.create() signature) while keeping nested values as typed Task / NotebookTask / etc. dataclasses that satisfy .as_dict().
3. this is the same pattern already used by update_job_settings() in the same class.

changes:

• dbt/adapters/databricks/api_client.py - WorkflowJobApi.create() now deserializes the dict via JobSettings.from_dict() and passes .as_shallow_dict() to the sdk. inline comment documents the sdk internals that make this the correct choice.
• tests/unit/api_client/test_workflow_job_api.py - tests strengthened to assert isinstance(task, Task), call .as_dict() on each task and verify output (directly proving the original AttributeError cannot recur), and add a new test_create__invalid_job_spec_raises covering the JobSettings.from_dict() error path.

checklist

• i have run this code in development and it appears to resolve the stated issue
• this pr includes tests, or tests are not required/relevant for this pr
• i have updated the CHANGELOG.md and added information about my change to the "dbt-databricks next" section.

[github-actions]

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File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
dbt/adapters/databricks
api_client.py
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[sd-db]

Changes look good, thanks for the PR !