Trying to fix failing windows build

.github/workflows/tests.yml

@@ -52,6 +52,8 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
+        # don't build stuff from source
+        pip install wheel
         pip install -r requirements/requirements.txt
         pip install -r requirements/test_requirements.txt
         # work around issues with GPy setting matplotlib backend