benchmark: keep decimals in results

Some benchmarks' results are small values, so keeping decimals when running them manually (not comparing) can be helpful.

Lint: https://ci.nodejs.org/job/node-test-linter/6124/ Lint: https://ci.nodejs.org/job/node-test-linter/6125/

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines

Affected core subsystem(s)

• benchmark