Update python-app.yml

.github/workflows/python-app.yml

@@ -23,7 +23,7 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        pip install pyqt5 pyinstaller
+        pip install pyqt5 pyinstaller flake8
         if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
     
     - name: Lint with flake8