Fix os versions

.github/workflows/python-app.yml

@@ -33,7 +33,7 @@ jobs:
       run: |
         python -m pip install --upgrade pip
         pip install flake8 pytest
-        if -f requirements.txt ; then pip install -r requirements.txt; fi
+        pip install -r requirements.txt
     - name: Lint with flake8
       run: |
         # stop the build if there are Python syntax errors or undefined names