test: mark test-fs-stat-bigint as flaky

Refs: https://github.com/nodejs/node/issues/24593
PR-URL: https://github.com/nodejs/node/pull/28156


Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>