GPU runner for pytests during CI

[watiss]

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The idea is that we want to run our unit tests (pytests), and probably more end-to-end tests as well as performance benchmarks on GPU's for our releases instead of just relying on CPU like we do now. Some things may work on CPU but not on GPU. Some ideas are:

• Get a runner going on our cluster and use that for free.
• Run it on AWS or Azure or Google.

Look into what these do: pytorch, pytorch lightning, deepchem, torchdrug