prevent WordPress from sending emails when the auto update is successful

rkv-bypass-auto-update.php

<?php
/**
 * bypass the notification email on successful auto-updates
 *
 * @param  [type] $send        [description]
 * @param  [type] $type        [description]
 * @param  [type] $core_update [description]
 * @param  [type] $result      [description]
 * @return [type]              [description]
 */
function rkv_bypass_auto_update_email( $send, $type, $core_update, $result ) {
	return ! empty( $type ) && $type == 'success' ? false : true;
}

add_filter( 'auto_core_update_send_email', 'rkv_bypass_auto_update_email', 10, 4 );