test: update test-timers-block-eventloop.js

When CPU is busy, the above sequential case fails occasionally,
expand the timeout value to fix it.

PR-URL: https://github.com/nodejs/node/pull/16314
Fixes: https://github.com/nodejs/node/issues/16310


Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>