Run unittests with and without the faiss library.

faiss is now an optional package for GPyTorch, to be used in conjunction with the
VNNGP model (#2026) and hopefully more nearest neighbor GP methods in the future.
This PR ensures that our test suite tests the functionality of GPyTorch with and
without the faiss library.

Author: gpleiss

.github/workflows/run_test_suite.yml

@@ -37,9 +37,13 @@ jobs:
     strategy:
       matrix:
         pytorch-version: ["master", "stable"]
-        pyro: ["with-pyro", "no-pyro"]
+        extras: ["with-extras", "no-extras"]
     steps:
     - uses: actions/checkout@v2
+    - uses: conda-incubator/setup-miniconda@v2  # Necessary to install faiss
+      with:
+        auto-update-conda: false
+        python-version: "3.7"
     - name: Set up Python
       uses: actions/setup-python@v2
       with:
@@ -51,8 +55,9 @@ jobs:
         else
           pip install torch==1.10+cpu -f https://download.pytorch.org/whl/torch_stable.html;
         fi
-        if [[ ${{ matrix.pyro }} == "with-pyro" ]]; then
+        if [[ ${{ matrix.extras }} == "with-extras" ]]; then
           pip install "pyro-ppl>=1.8";
+          conda install -c pytorch faiss-cpu
         fi
         pip install -r requirements.txt
     - name: Run unit tests