upgrade checkout and setup-python actions

Author: graingert

.github/workflows/main.yml

@@ -18,10 +18,10 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v1
+        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 }}