Administration: Invalid argument passed in additional_classes.

Fix `additional_classes` argument passed as a string instead of an array. Follow up to [56409].

Props joedolson.
See #57791.

git-svn-id: https://develop.svn.wordpress.org/trunk@56410 602fd350-edb4-49c9-b593-d223f7449a82

Author: joedolson

src/wp-admin/includes/network.php

@@ -445,7 +445,7 @@ function network_step2( $errors = false ) {
 		$notice_message = '<strong>' . __( 'Caution:' ) . '</strong> ';
 		$notice_args    = array(
 			'type'               => 'warning',
-			'additional_classes' => 'inline',
+			'additional_classes' => array( 'inline' ),
 		);
 
 		if ( file_exists( $home_path . '.htaccess' ) ) {