posts before today

// WP_Query arguments
$args = array(
	'post_type'              => array( 'corso' ),
	'post_status'            => array( 'publish' ),
	'date_query'             => array(
		array(
			'before'        => 'today',
		),
	),
);

// The Query
$query = new WP_Query( $args );