test: s/assert.notEqual()/assert.notStrictEqual()/

PR-URL: https://github.com/nodejs/node/pull/10541


Reviewed-By: Sam Roberts <vieuxtech@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Italo A. Casas <me@italoacasas.com>