Fix BigQueryToMsSqlOperator documentation (#18995)

Co-authored-by: Aaron Mangum <aaron.mangum@iherb.com>

airflow/providers/google/cloud/transfers/bigquery_to_mssql.py

@@ -44,13 +44,14 @@ class BigQueryToMsSqlOperator(BaseOperator):
 
        transfer_data = BigQueryToMsSqlOperator(
             task_id='task_id',
-            dataset_table='origin_bq_table',
+            source_project_dataset_table='my-project.mydataset.mytable',
             mssql_table='dest_table_name',
             replace=True,
         )
 
-    :param dataset_table: A dotted ``<dataset>.<table>``: the big query table of origin
-    :type dataset_table: str
+    :param source_project_dataset_table: A dotted ``<project>.<dataset>.<table>``:
+        the big query table of origin
+    :type source_project_dataset_table: str
     :param selected_fields: List of fields to return (comma-separated). If
         unspecified, all fields are returned.
     :type selected_fields: str