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: #23038
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

Author: addaleax

test/sequential/test-fs-watch-system-limit.js

@@ -42,7 +42,8 @@ gatherStderr.on('data', common.mustCallAtLeast((chunk) => {
   if (accumulated.includes('Error:') && !finished) {
     assert(
       accumulated.includes('ENOSPC: System limit for number ' +
-                           'of file watchers reached'),
+                           'of file watchers reached') ||
+      accumulated.includes('EMFILE: '),
       accumulated);
     console.log(`done after ${processes.length} processes, cleaning up`);
     finished = true;