test: exclude new fs watch test for AIX

As per #5085
exclude new test from AIX until we have fixes for
libuv for fs watching on AIX.  Excluding test
so AIX tests are green and we don't miss
other regressions

PR-URL: #5937
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

test/parallel/parallel.status

@@ -24,3 +24,4 @@ test-tick-processor           : PASS,FLAKY
 # regressions until this work is complete
 [$system==aix]
 test-fs-watch-enoent                 : FAIL, PASS
+test-fs-watch-encoding               : FAIL, PASS