CI: Spot fixes related to nightly and stable PyTorch builds (#2190)

* CI: Skip (redundant) libtorch build when using stable PyTorch version

When we use PyTorch stable builds, there is no need to build libtorch
from source, making the stable-pytorch-with-torch-binary-OFF
configuration redundant with stable-pytorch-with-torch-binary-ON.  This
patch drops the redundant configuration from CI.

* CI: Simplify guard conditions for creating and using libtorch cache

Whether libtorch is enabled or not is predicated on a host of conditions
such as the platform, in-tree versus out-of-tree build, and stable
versus nightly PyTorch builds.  Instead of repeating these conditions to
guard whether to create or use the libtorch cache artifacts (and getting
them almost incorrect), this patch predicates the relevant pipeline
steps to whether libtorch is enabled, thus making the conditions far
simpler.

.github/workflows/buildAndTest.yml

@@ -45,6 +45,9 @@ jobs:
             llvm-build: out-of-tree
           - os-arch: windows-x86_64
             torch-version: stable
+          # For PyTorch stable builds, we don't build PyTorch from source
+          - torch-version: stable
+            torch-binary: OFF
         include:
           # Specify OS versions
           - os-arch: ubuntu-x86_64
@@ -89,7 +92,7 @@ jobs:
         arch: x64
 
     - name: Try to Restore PyTorch Build Cache
-      if: matrix.os-arch != 'windows-x86_64'
+      if: ${{ matrix.torch-binary == 'OFF' }}
       id: cache-pytorch
       uses: actions/cache/restore@v3
       with:
@@ -147,7 +150,7 @@ jobs:
       run: ./build_tools/python_deploy/build_windows_ci.sh
 
     - name: Save PyTorch Build Cache
-      if: ${{ github.ref_name == 'main' && matrix.torch-binary == 'OFF' && matrix.os-arch != 'windows-x86_64' }}
+      if: ${{ github.ref_name == 'main' && matrix.torch-binary == 'OFF' }}
       uses: actions/cache/save@v3
       with:
         path: ${{ github.workspace }}/build_tools/python_deploy/wheelhouse