test: refactor test-tls-ocsp-callback

Checklist

• [x ] make -j8 test (UNIX), or vcbuild test nosign (Windows) passes
• [x ] tests and/or benchmarks are included
• [x ] commit message follows commit guidelines

Affected core subsystem(s)

test

Description of change

refactor all var to either const/let change all assert.equal to assert.strictEqual change all assert.ok(...===...) to assert.strictEqual