Updating cluster results in change to gateway_api_config.channel to null

The following plan occurs even if no changes have been made to the Terraform config. This appears to be a slight change in GCP's GKE implementation, and when applied, GCP changes the null value back to CHANNEL_STANDARD, so there are no adverse affects.

        gateway_api_config {
          - channel = "CHANNEL_STANDARD" -> null
        }