subsystem: fix error in test-cluster-worker-death.js

[bruceplai]

Checklist

• make -j8 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)

Description of change

Replaced calls to assert.equal with assert.strictEqual in order
to fix the following error:
"Please use assert.strictEqual() instead of assert.strictEqual()"

[imyller]

@bruceplai Please replace subsystem: with test: in commit message. Thank you 👍

[bruceplai]

Will fix commit title in another pull request.