test: make test-tick-processor.js non-flaky

Checklist

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

Affected core subsystem(s)

test

Description of change

Wait for a sought-for symbol to appear instead of just hard-killing subprocesses at 2s timeout.

Fix: #4427 (closed)