use python container, remove setup-python

.github/workflows/python-test.yml

@@ -9,13 +9,10 @@ on:
 jobs:
   build:
     runs-on: "ubuntu-latest"
+    container: python:latest
 
     steps:
       - uses: actions/checkout@v2
-      - name: Set up Python
-        uses: actions/setup-python@v4
-        with:
-          python-version: "3.9.12"
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip