test: loosen test for negative timestamps in `test-fs-stat-date`
One more attempt to make test from https://github.com/nodejs/node/pull/43714 pass on v16.x-staging and avoid similar test failures on main in the future.
If filesystem doesn't support negative timestamps and stat returns 0, print a warning and proceed.
cc @targos
CI: https://ci.nodejs.org/job/node-test-pull-request/46648/
CI: https://ci.nodejs.org/job/node-test-pull-request/46655/
CI: https://ci.nodejs.org/job/node-test-pull-request/46665/
@nodejs/testing @nodejs/fs
Landed in 8f8ce2505d2d9e0124398640b1fe17beee282014