test: fix `common.mustCall` `length` and `name` properties

Reassign `name` and `length` properties to the returned function to not
break code that relies on it.

PR-URL: https://github.com/nodejs/node/pull/38464


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>