timers: fix eventloop block

When there are at least 2 timers set by setInterval whose callback execution are longer than interval, the eventloop will be blocked.

This commit fix the above bug.

Fixes: https://github.com/nodejs/node/issues/15068

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)