add pytest to cpp ci workflow

Author: mreso

.github/workflows/ci-cpu-cpp.yml

@@ -55,3 +55,6 @@ jobs:
         run: |
           cd cpp && rm -rf _build && sudo mkdir /mnt/_build && sudo chmod 777 /mnt/_build && mkdir _build && sudo mount --bind /mnt/_build _build
           ./build.sh
+      - name: Run test
+        run: |
+          cd .. && pytest test/pytest/test_cpp_backend.py