Fix some erroneous @param annotations.

See #30799.


git-svn-id: https://develop.svn.wordpress.org/trunk@31219 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/query.php

@@ -1271,6 +1271,7 @@ class WP_Query {
 	 *
 	 * @since 3.1.0
 	 * @access private
+	 * @var bool|string
 	 */
 	private $query_vars_hash = false;