Docs: Add the parameter name for the wp_roles_init action.

[39082] missed adding the name of the parameter to the docs of the `wp_roles_init` action.

Props johnbillion for the catch.
See #23016.



git-svn-id: https://develop.svn.wordpress.org/trunk@39083 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-roles.php

@@ -133,7 +133,7 @@ class WP_Roles {
 		 *
 		 * @since 4.7.0
 		 *
-		 * @param WP_Roles A reference to the WP_Roles object.
+		 * @param WP_Roles $this A reference to the WP_Roles object.
 		 */
 		do_action( 'wp_roles_init', $this );
 	}