test: changed function to arrow function

Convert callback functions that are anonymous
to arrow functions for better readability.
Also adjusted the `this` object in places where
that was required.

PR-URL: https://github.com/nodejs/node/pull/32875


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>