test: mark two tests as flaky in AIX

sequential/test-inspector-debug-end and
parallel/test-child-process-execfile

Off late these have been failing in AIX. Debugging core dump
suggested that this is a side effect of exit-race that is
described in https://github.com/nodejs/node/issues/25007
Mart these  as flaky in AIX until that is resolved.

Refs: https://github.com/nodejs/node/issues/25047
Refs: https://github.com/nodejs/node/issues/25029

PR-URL: https://github.com/nodejs/node/pull/25126


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>