Remove __cleanenv from PEP-657 tests

[ammaraskar]

This should help fix the failures in the shared buildbots caused by #27023

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @isidentical for commit 6421c7d 🤖

If you want to schedule another build, you need to add the ":hammer: test-with-buildbots" label again.

[ammaraskar]

Here's the ubuntu shared run, this will be the key one to look at: https://buildbot.python.org/all/#/builders/500/builds/88

[pablogsal]

Here's the ubuntu shared run, this will be the key one to look at: https://buildbot.python.org/all/#/builders/500/builds/88

Merging as this is passing now