Update python-app.yml

Author: bhimrazy

.github/workflows/python-app.yml

@@ -22,7 +22,7 @@ jobs:
     - name: Set up Python
       uses: actions/setup-python@v3
       with:
-        python-version: "3.x"
+        python-version: "3.9"
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip