Pin pytorch version for OSX tests.

Current version of pytorch (12.0.1) ships a specific openmp runtime on
OSX, which conflicts with the system one. This workaround fixes Faiss'
CI until pytorch is fixed, but it does not fix the incompatibility
itself.

conda/faiss/meta.yaml

@@ -73,7 +73,8 @@ outputs:
       requires:
         - numpy
         - scipy
-        - pytorch
+        - pytorch  # [not osx]
+        - pytorch <1.12.0  # [osx]
       commands:
         - python -X faulthandler -m unittest discover -v -s tests -p "test_*"
         - python -X faulthandler -m unittest discover -v -s tests -p "torch_*"