For doc block types, favor bool over the few remaining booleans

See #32444.


git-svn-id: https://develop.svn.wordpress.org/trunk@32964 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/theme.php

@@ -1159,7 +1159,7 @@ function get_random_header_image() {
  * @since 3.2.0
  *
  * @param string $type The random pool to use. any|default|uploaded
- * @return boolean
+ * @return bool
  */
 function is_random_header_image( $type = 'any' ) {
 	$header_image_mod = get_theme_mod( 'header_image', get_theme_support( 'custom-header', 'default-image' ) );