timers: fix refreshed timers exiting too early

If a timer is refreshed in its callback, we should not decrease refCount to prevent exiting event loop ahead of time.

Fixes: https://github.com/nodejs/node/issues/26642

Checklist

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