test: fix flaky interval test

PR-URL: https://github.com/nodejs/node/pull/18161
Fixes: https://github.com/nodejs/node/issues/18160


Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>