(prefect-dbt)Fix source freshness logs routing to flow instead of enclosing task

[vyagubov]

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closes #22990

When PrefectDbtRunner.invoke(['source', 'freshness', ...]) is called inside a Prefect task, logs from source node events were routed to the flow run instead of the enclosing task.

Root cause:

_process_logging_sync always called task_state.get_task_logger(node_id, ...) for any event with node_info. For dbt build this works fine — a Prefect task is registered per model node via _process_node_started_sync. But _get_manifest_node_and_config only looks in manifest.nodes, not manifest.sources, so source nodes during source freshness never get a task registered. get_task_run_id(node_id) returns None, the logger is created with task_run_id=None, and Prefect routes those logs to the flow.

Meanwhile events without node_info (e.g. dbt startup lines) already fell back to hydrated_context(context) + get_run_logger(), which correctly restores the caller's task run context — that's why dbt deps logs appeared in the task but source freshness per-source logs did not.

[vyagubov]

Tested in local environment manually. I ran dbt run, dbt build, and dbt source freshness. All finished successfully, logs are as expected.

One CI test failed — it appears unrelated to this change (a google-protobuf import error).

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.