AIP-84 - remove dry_run in post backfill tests

[rawwar]

I noticed a dry_run argument being sent in creating backfill tests. It's not part of the request body as per

airflow/airflow/api_fastapi/core_api/datamodels/backfills.py

Lines 26 to 35 in d460972

	class BackfillPostBody(BaseModel):
	"""Object used for create backfill request."""
	dag_id: str
	from_date: datetime
	to_date: datetime
	run_backwards: bool = False
	dag_run_conf: dict = {}
	reprocess_behavior: ReprocessBehavior = ReprocessBehavior.NONE
	max_active_runs: int = 10

We can either add it to the model(but I don't see it being utilized by underlying functionality) or remove it from tests.

Found this issue while working on #44306

[pierrejeambrun]

Indeed,thanks.

There is a dedicated endpoint for running backfills in dry_run mode.