When you edit wp-config.php the second time – when the installer tells you to update your wp-config.php file with a bunch of multisite-related includes – at this point remove the definition for WP_ALLOW_MULTISITE.
REMOVE this line:
define('WP_ALLOW_MULTISITE', true);
based on your example above, you’d be left with:
/* Multisite */
define('WP_ALLOW_MULTISITE', true);
define('MULTISITE', true);
define('SUBDOMAIN_INSTALL', false);
define('DOMAIN_CURRENT_SITE', 'test.site.com');
define('PATH_CURRENT_SITE', "https://wordpress.stackexchange.com/");
define('SITE_ID_CURRENT_SITE', 1);
define('BLOG_ID_CURRENT_SITE', 1);
Once I did that, I logged back in and suddenly the “My sites” menu appeared!