Correct references of @uses $wpdb in core documentation to use @global.

See #30191, [30105].
Fixes #30217.


git-svn-id: https://develop.svn.wordpress.org/trunk@30122 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-admin/includes/schema.php

@@ -324,7 +324,8 @@ $wp_queries = wp_get_db_schema( 'all' );
  * Create WordPress options and set the default values.
  *
  * @since 1.5.0
- * @uses $wpdb
+ *
+ * @global wpdb $wpdb WordPress database abstraction object.
  * @uses $wp_db_version
  */
 function populate_options() {