fix python version as string in actions/setup-python@v4

.github/workflows/python-app.yml

@@ -73,7 +73,7 @@ jobs:
       - name: Set up Python 3.10
         uses: actions/setup-python@v4
         with:
-          python-version: 3.10
+          python-version: "3.10"
       - name: Install flit
         run: pip install flit
       - name: Build package