always use the latest stable version when releasing (#106)

* rename step

* automatically update python whenever necessary

.github/workflows/pypipublish.yml

@@ -15,10 +15,10 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@v4
-      - name: Set up Python 3.9
+      - name: Set up Python
         uses: actions/setup-python@v5
         with:
-          python-version: "3.9"
+          python-version: "3.x"
       - name: Install publish dependencies
         run: python -m pip install build
       - name: Build package