avoid deprecation warnings in BigQuery transfer operators

[eladkal]

bigquery_conn_id is deprecated:

airflow/airflow/providers/google/cloud/hooks/bigquery.py

Lines 107 to 114 in f62e690

	if bigquery_conn_id:
	warnings.warn(
	"The bigquery_conn_id parameter has been deprecated. You should pass "
	"the gcp_conn_id parameter.",
	DeprecationWarning,
	stacklevel=2,
	)
	gcp_conn_id = bigquery_conn_id

avoid setting this parameter in transfer operators

closes: #20437

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