TST: be stricter when checking wheel contents

[dnicolodi]

There is no reason to allow uncertainty whether directory entries are present or not in the wheel files. For simplicity, directory entries are not added the wheel files, thus the tests require no adjustment.

[rgommers]

LGTM, thanks. Checked where this came from, and it's a leftover from very early on when we were still using auditwheel directly (see commit message of commit 2d203c0).

[dnicolodi]

Checked where this came from, and it's a leftover from very early on when we were still using auditwheel directly

Yes, I saw that. However, I would argue that the behaviour had to be deterministic back then too, thus filtering out directory entries was done just for minor convenience in writing the tests, rather than real changes between test runs. I didn't want to go into the details in the commit message.