Build with nightly Torch instead of the latest

Summary:
Changes in the PyTorch C++ layer affect Monarch's tensor engine builds. Without this change, the CI builds will pick up the latest PyTorch through build-requirements.txt. This diff removes this dependency.

We see this affecting #1680

Differential Revision: D85670693

Author: allenwang28

.github/workflows/build-cuda.yml

@@ -33,6 +33,7 @@ jobs:
 
         # Setup build environment (conda + system deps + rust + build deps)
         setup_build_environment
+        setup_pytorch_with_headers "${{ matrix.gpu-arch-version }}" "${{ matrix.torch-spec }}"
 
         # Setup Tensor Engine
         setup_tensor_engine

build-requirements.txt

@@ -1,4 +1,5 @@
-torch
+# torch is also a dependency here, but we want to ensure that
+# we're building against the PyTorch index for nightly.
 setuptools
 setuptools-rust
 wheel