TorchScript-related test failures under PyTorch 2.0

[eb8680]

From #3192, the following torch.jit-related tests are failing for torch>=2.0.0:

• [ ] tests/contrib/test_minipyro.py::test_elbo_jit[minipyro] (traceback)
• [ ] tests/contrib/cevae/test_cevae.py::test_serialization[jit-exponential-1] (traceback)
• [ ] tests/contrib/cevae/test_cevae.py::test_serialization[jit-exponential-2] (traceback)
• [ ] tests/contrib/test_minipyro.py::test_elbo_equivalence

The first test may just need to have a tolerance tweaked. The second and third may not be worth fixing unless it's super easy.

These can probably be xfailed rather than blocking a PyTorch 2.0 compatibility release.