auto detect number of workers.

use auto detect for number of pytest workers

.github/workflows/test-models.yml

@@ -30,6 +30,8 @@ jobs:
       run: |
         python -m pip install --upgrade pip
         python -m pip install flake8 pytest
+        if [ -f requirements.txt ]; then pip install -r requirements.txt --extra-index-url https://download.pytorch.org/whl/nightly/cpu  -f https://github.com/llvm/torch-mlir/releases -f https://github.com/nod-ai/SHARK-Runtime/releases; fi
+
     - name: Lint with flake8
       run: |
         # stop the build if there are Python syntax errors or undefined names
@@ -41,4 +43,4 @@ jobs:
         cd $GITHUB_WORKSPACE
         ./setup_venv.sh
         source shark.venv/bin/activate
-        pytest
+        pytest --workers auto