Update python-app.yml

.github/workflows/python-app.yml

@@ -37,7 +37,7 @@ jobs:
       run: |
         python -m pip install --upgrade pip
         pip install flake8 pytest
-        if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
+        if ( -f requirements.txt ); then pip install -r requirements.txt; fi
         pip install onnxruntime==1.15
         pip install onnxmltools
         pip install onnx==${{ matrix.onnx-version }}