Docs: Add a missing return description for `get_post_taxonomies()`.

h/t deeptiboddapati.
See #39130.


git-svn-id: https://develop.svn.wordpress.org/trunk@40298 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/taxonomy.php

@@ -3993,7 +3993,7 @@ function get_the_taxonomies( $post = 0, $args = array() ) {
  * @since 2.5.0
  *
  * @param int|WP_Post $post Optional. Post ID or WP_Post object. Default is global $post.
- * @return array
+ * @return array An array of all taxonomy names for the given post.
  */
 function get_post_taxonomies( $post = 0 ) {
 	$post = get_post( $post );