Force UTF-8 in load-styles.php, like we do in load-scripts.php.

props iamfriendly, mjbanks.
fixes #25012.
Built from https://develop.svn.wordpress.org/trunk@27253


git-svn-id: http://core.svn.wordpress.org/trunk@27110 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/load-styles.php

@@ -134,7 +134,7 @@ foreach( $load as $handle ) {
 	}
 }
 
-header('Content-Type: text/css');
+header('Content-Type: text/css; charset=UTF-8');
 header('Expires: ' . gmdate( "D, d M Y H:i:s", time() + $expires_offset ) . ' GMT');
 header("Cache-Control: public, max-age=$expires_offset");