Switch to setup-python v2 in CI

Author: flashcode

.github/workflows/ci.yml

@@ -27,7 +27,7 @@ jobs:
       - uses: actions/checkout@v2
 
       - name: Set up Python ${{ matrix.python-version }}
-        uses: actions/setup-python@v1
+        uses: actions/setup-python@v2
         with:
           python-version: ${{ matrix.python-version }}