Fix dags test DagRun start date

[bobu-putheeckal]

Fixes #66127

DAG.test() currently passes start_date=logical_date or run_after when creating the test DagRun. When airflow dags test is invoked with an old logical date, the DagRun start date is recorded as that logical date, which inflates the reported run duration.

This changes DAG.test() to use run_after as the DagRun start date while preserving the requested logical date, and adds a regression test for the CLI path.

Testing:

• python3 -m py_compile airflow-core/tests/unit/cli/commands/test_dag_command.py task-sdk/src/airflow/sdk/definitions/dag.py
• git diff --check
• Targeted pytest could not be run locally because the system pytest is too old for Airflow's current tests_common plugin; full uv setup needs Java for jpype1/JDBC provider.

[boring-cyborg]

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