Use actions/setup-python@v2 to deploy latest

This should fix an error with Python 3.9.

.github/workflows/deploy-latest.yml

@@ -12,7 +12,7 @@ jobs:
     - name: Check out datasette
       uses: actions/checkout@v2
     - name: Set up Python
-      uses: actions/setup-python@v1
+      uses: actions/setup-python@v2
       with:
         python-version: 3.9
     - uses: actions/cache@v2