Get the tests passing against Windows

> OK, the tests do NOT pass against Windows! https://github.com/simonw/datasette/runs/5044105941
>
> <img width="767" alt="image" src="https://user-images.githubusercontent.com/9599/152265501-5b5af51b-0fae-4aa7-b86d-7b61aba24b3c.png">

_Originally posted by @simonw in https://github.com/simonw/datasette/issues/1626#issuecomment-1028515161_