Add a missing `@return` tag and description to the DocBlock for `WP_Theme::scandir()`.

Props lamosty.
Fixes #31872.


git-svn-id: https://develop.svn.wordpress.org/trunk@32345 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-theme.php

@@ -998,6 +998,8 @@ final class WP_Theme implements ArrayAccess {
 	 * @param string            $relative_path Optional. The basename of the absolute path. Used to control the
 	 *                                         returned path for the found files, particularly when this function
 	 *                                         recurses to lower depths. Default empty.
+	 * @return array|false Array of files, keyed by the path to the file relative to the `$path` directory prepended
+	 *                     with `$relative_path`, with the values being absolute paths. False otherwise.
 	 */
 	private static function scandir( $path, $extensions = null, $depth = 0, $relative_path = '' ) {
 		if ( ! is_dir( $path ) )