CI: Figure out a fast way to install dependencies on PyPy

[rht]

What's the problem this feature will solve? The CI for PyPy has been always failing since the requirements update. I remembered that PyPy install, if not yet cache, takes a very long time. We have to resort to disabling PyPy, because we can't have the CI timeout to be too long.

Describe the solution you'd like There should be a fast way to install the dependencies on PyPy. Maybe via Conda. Not sure.