test: fix flaky sequential/test-fs-watch-system-limit

This test has at least once locally received `EMFILE` rather
than `ENOSPC`, which also seems to provide a reasonable error
message (which is what the test ultimately checks).

PR-URL: https://github.com/nodejs/node/pull/23038


Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>