When DAGs use the new Airflow 3.x recommended import style
`from airflow.sdk import Variable`, the existing monkey patch for
`airflow.models.Variable.get` was not being applied. This caused
`astro dev parse` to fail with "Variable not found" errors when using
remote backends like Azure Key Vault.

This fix extends the Variable.get monkey patch to also apply to
`airflow.sdk.Variable`, ensuring DAG parsing works correctly for both
the legacy `airflow.models.Variable` and the new `airflow.sdk.Variable`
import styles.

Fixes PM-804

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>