tests: Skip PyPy tests on Windows

[Mickaël Schoentgen]

Let's skip PyPy tests on Windows until we find a way to make them work.

That issue can be used to skip those tests at first, and as an investigation/fix ticket in a second time.

cc @altendky

[Kyle Altendorf]

#976

[Marc Abramowitz]

Can this be closed since #976 was merged?

[Mickaël Schoentgen]

Ideally, in a second time, we can find a way to fix issues and enable back those tests.