Install PyTorch in unittest-macos even in Buck mode

We've been seeing flakes due to missing torchgen that have become more common. After some investigation, it appears that #8688 was probably overzealous: installing pytorch was probably also installing torchgen, so let's install pytorch.

Test Plan: unittest-buck / macos on this PR, monitor to see if failures go away.

ghstack-source-id: 05496b1
ghstack-comment-id: 2744469219
Pull Request resolved: #9505

Author: swolchok

.ci/scripts/unittest-macos.sh

@@ -34,6 +34,10 @@ if [[ "$BUILD_TOOL" == "cmake" ]]; then
 
     .ci/scripts/unittest-macos-cmake.sh
 elif [[ "$BUILD_TOOL" == "buck2" ]]; then
+    (
+        source .ci/scripts/utils.sh
+        install_pytorch_and_domains
+    )
     .ci/scripts/unittest-buck2.sh
     # .ci/scripts/unittest-macos-buck2.sh
 else