Use pytest-randomly to randomly order tests

[dcherian]

https://github.com/pytest-dev/pytest-randomly

prompted by #10327 (comment)

[keewis]

good idea in general, but in the particular case I don't think that will help: it's the same operation that emits different errors depending on internal state (I suspect there's a set involved somewhere, i.e. the state changes with interpreter instances), which means the same test may have different results between runs

[dcherian]

Yes won't catch that one but I was curious about others. Looks like every env fails with a different error!