Docs: Improve documentation for _prime_post_parents_caches().

Add in missing since PHPDoc block for `_prime_post_parents_caches` function added in [56763].

Props mukesh27.
See #59188

git-svn-id: https://develop.svn.wordpress.org/trunk@56773 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/post.php

@@ -7801,6 +7801,8 @@ function _prime_post_caches( $ids, $update_term_cache = true, $update_meta_cache
  *
  * @global wpdb $wpdb WordPress database abstraction object.
  *
+ * @since 6.4.0
+ *
  * @param int[] $ids ID list.
  */
 function _prime_post_parents_caches( array $ids ) {