Unfortunately, Windows' scheduler means that test timeouts get hit very
easily, because it seems the system can refuse to schedule a waiting
process for *upwards of 10 minutes*. We should look for a better
solution for this problem going forwards, but for now, just give Windows
a very high test timeout.

The 30 minute timeout set here is around the duration of a *full CI run*
on Windows, so it should be impossible to hit normally, but it means
that if a test gets stuck we'll at least get told (eventually).