PHP Fatal if $query->get( 'order' ) is an array

[kingkool68]

Description of the bug

In

searchpress/lib/class-sp-integration.php

Lines 297 to 303 in b90a875

	// Set sort ordering.
	$order = strtolower( $query->get( 'order' ) );
	if ( ! empty( $order ) ) {
	if ( in_array( $order, [ 'asc', 'desc' ], true ) ) {
	$es_wp_query_args['order'] = $order;
	}
	}

the order value of the query gets passed directly to strtolower(). It's possible for the order parameter of WP_Query to be an array and SearchPress currently can't handle that.

Steps To Reproduce

Run query like this:

$query = new WP_Query([
	'orderby' => [ 'title', 'date' ],
	'order'     => [ 'DESC', 'ASC' ],
]);

Additional Information

No response