Update flake.yml updated to 3.9

Author: brovelli

.github/workflows/flake.yml

@@ -15,7 +15,7 @@ jobs:
       - name: Set up Python 🔧
         uses: actions/setup-python@v4
         with:
-          python-version: '3.7'
+          python-version: '3.9'
 
       - name: Install dependencies 🔧
         run: |