test: mark test-fs-stat-bigint flaky on FreeBSD

Refs: https://github.com/nodejs/node/issues/31727

PR-URL: https://github.com/nodejs/node/pull/31728


Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Denys Otrishko <shishugi@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>