New review comment by ahesford on void-packages repository

https://github.com/void-linux/void-packages/pull/43946#discussion_r1218216356

Comment:
I just ran into the reason for the cleanup: attempting to re-run a check after a failure will cause `python3 -m installer` to fail unless the test directory is clean. Still, I think the idea of purging a (typically nonexistent) directory just to avoid issues with re-running tests is strange. At this point, I guess I'd rather see
```sh
local testdir="${wrksrc}/.xbps-testdir/$(date +s)"
```
and skip cleanup altogether. This should solve the problem of `pytest` trying to traverse into `tmp` without requiring a manual exclude, keeps our tests in a more-likely-unique subdirectory that should not conflict with any package contents, and avoid strange pre-clean steps. As a bonus, if you *do* run multiple tests to correct a failure, you can always do something like
```sh
diff -r .xbps-testdir/<failed> .xbps-testdir/<succeeeded>
```
after the fact to confirm what, if anything, has changed in the installed wheel.