test: mark test-tty-wrap as flaky for AIX

We have had nodejs#9728
open for a while but the frequency of the failures
seems to be such that we should mark it as flaky
while we continue to investigate.

PR-URL: nodejs#10618
Reviewed-by: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/pseudo-tty/pseudo-tty.status

@@ -4,3 +4,5 @@ prefix pseudo-tty
 # test issue only, covered under https://github.com/nodejs/node/issues/7973
 no_dropped_stdio           : SKIP
 no_interleaved_stdio       : SKIP
+# being investigated under https://github.com/nodejs/node/issues/9728
+test-tty-wrap              : FAIL, PASS