test: use Number.isNaN()

PR-URL: https://github.com/nodejs/node/pull/17319


Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: Khaidi Chu <i@2333.moe>
Reviewed-By: James M Snell <jasnell@gmail.com>