unittest discovery and test.regrtest cannot find tests when they're not on the filesystem

Bug report

Bug description:

When the standard library is a zip archive on sys.path, the test package is not a directory: findtests() failed with an OSError from os.listdir() and load_package_tests() failed with "Start directory is not importable" from unittest discovery.

I'm still deciding if this should be done, it is perhaps odd thing to do to bundle tests into an archive before running, but this should apply to other import hooks as well and bundling tests into a zip is sort of a nice way of running tests against a fully zipped application. It's a feature regardless.

Linked PRs

• gh-157145

Inizia esaminando unittest discovery e test.regrtest, quindi riproduci il malfunzionamento con la libreria standard in un archivio ZIP su sys.path. Il lavoro è completato quando test discovery e regrtest riescono a individuare ed eseguire i test tramite hook di importazione non basati sul filesystem; gh-157145 è il PR collegato da esaminare per primo.