test: fix unreliable async-hooks/test-signalwrap
Use an interval to keep the event loop open so the test does not exit
before receiving all signals fom asynchronous exec()
calls.
Fixes: https://github.com/nodejs/node/issues/14070
Checklist
-
make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
commit message follows commit guidelines
Affected core subsystem(s)
test async_hooks