test: fix a TODO and remove obsolete TODOs

This removes outdated TODOs and adds a test for invalid input in
`fs.copyFile` and solves a TODO by doing so.

PR-URL: https://github.com/nodejs/node/pull/20319


Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>