Changes to List a webhook delivery’s attempts.

removed the non-success response with the status 409

removed the non-success response with the status 429

the response property attempts became required for the status 200

the response property attempts/items/attempt became required for the status 200

the response property attempts/items/attempted_at became required for the status 200

the response property attempts/items/error became required for the status 200

the response property attempts/items/status_code became required for the status 200

the response property total became required for the status 200