Docs: Add a `@global` entry for `$wp_filter` in `wp_start_object_cache()`.

Props bhaveshkhadodara.
Fixes #41222.

git-svn-id: https://develop.svn.wordpress.org/trunk@40992 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/load.php

@@ -470,6 +470,8 @@ function wp_using_ext_object_cache( $using = null ) {
  *
  * @since 3.0.0
  * @access private
+ *
+ * @global array $wp_filter Stores all of the filters.
  */
 function wp_start_object_cache() {
 	global $wp_filter;