benchmark: update iterations in benchmark/util/format.js
Refs: https://github.com/nodejs/node/issues/50571
Belowing are the score improvement after 10X iteration change:
util/format.js n=1000000
util/format.js type="string" n=1000000 percent=154.84%
util/format.js type="string-2" n=1000000 percent=150.37%
util/format.js type="number" n=1000000 percent=156.83%
util/format.js type="replace-object" n=1000000 percent=111.05%
util/format.js type="unknown" n=1000000 percent=164.63%
util/format.js type="no-replace" n=1000000 percent=174.30%
util/format.js type="no-replace-2" n=1000000 percent=168.45%
util/format.js type="many-%" n=1000000 percent=177.32%
util/format.js type="object-to-string" n=1000000 percent=139.61%
util/format.js type="object-%s" n=1000000 percent=110.67%