Fix DbtCloudRunJobOperator having false failures during deferred polling

[amoghrajesh]

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Was generative AI tooling used to co-author this PR?

• Yes

closes: #70398

Why?

Deferred DbtCloudRunJobOperator tasks failed within seconds of deferring with a misleading DbtCloudJobRunException: Job run <id> has failed, even though the dbt Cloud job kept running and completed successfully hours later.

What

DbtCloudHook.get_headers_tenants_from_connection() and get_job_details() resolved the connection through the hook's synchronous connection cached_property while running inside the triggerer's live event loop. That
path masks the connection's secret via a synchronous comms call, which asgiref rejects when called from a thread already running an event loop the resulting RuntimeError propagated up through the trigger and was surfaced by the operator as a job failure instead of the real (transient) error it was.

Both call sites now resolve the connection through the existing async safe get_async_connection() helper, sharing a cache slot with the sync connection cached_property so neither path performs a duplicate connection lookup. Also switched the file's Connection type import to the airflow.providers.common.compat.sdk compat shim (matching what
get_connection()/get_async_connection() actually return under Airflow 3), which let a stale # type: ignore[return-value] on the connection property be removed.

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