FIX: Switch from PyTorch nightly to stable release (2.9.0) with CUDA 12.8

- Remove --pre flag to avoid nightly builds
- Change from /nightly/ to stable cu128 index
- Fixes hash mismatch error in CI pipeline

Author: mmcky

.github/workflows/ci.yml

@@ -31,7 +31,7 @@ jobs:
       - name: Install JAX, Numpyro, PyTorch
         shell: bash -l {0}
         run: |
-          pip install --pre torch torchvision torchaudio --index-url https://download.pytorch.org/whl/nightly/cu128
+          pip install torch torchvision torchaudio --index-url https://download.pytorch.org/whl/cu128
           pip install pyro-ppl
           pip install --upgrade "jax[cuda12-local]==0.6.2"
           pip install numpyro pyro-ppl