Random failures in CI

[srittau]

We started getting random errors in CI, both when running mypy_test and when running stubtest against third-party packages. It always affects a few third-party packages (but each time different ones), and the errors look like this for each package:

/tmp/tmph9e27zwx/.venv--2976680824983557238/bin/python: No module named mypy

[AlexWaygood]

There's a PyPI outage today https://status.python.org/incidents/2zf08fkp0nd1

[srittau]

The incident is marked as resolved. I've merged main into #13614, lets see what happens.

[srittau]

The only remaining errors are genuine. Closing.