update python-package.yml

.github/workflows/python-package.yml

@@ -26,7 +26,9 @@ jobs:
       run: |
         python -m pip install --upgrade pip
         python -m pip install flake8 pytest numba torch
-        if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
+        $reqFile = "requirements.txt"
+        if (Test-Path $reqFile) { pip install -r $reqFile }
+      shell: pwsh
     - name: Lint with flake8
       run: |
         # stop the build if there are Python syntax errors or undefined names