Correct the parameter type for the $stylesheet parameter in the mce_css filter documentation.

Fixes #34721
Props hnle

Built from https://develop.svn.wordpress.org/trunk@35660


git-svn-id: http://core.svn.wordpress.org/trunk@35624 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/class-wp-editor.php

@@ -572,7 +572,7 @@ final class _WP_Editors {
 				 *
 				 * @since 2.1.0
 				 *
-				 * @param array $stylesheets Comma-delimited list of stylesheets.
+				 * @param string $stylesheets Comma-delimited list of stylesheets.
 				 */
 				$mce_css = trim( apply_filters( 'mce_css', implode( ',', $mce_css ) ), ' ,' );