Update CI config

* remove unneeded `CI: true` env var since it's already set by the runner
* update to `actions/setup-python@v2`
* remove `x64` architecture since it's the default

.github/workflows/ci.yml

@@ -1,7 +1,6 @@
 name: CI
+
 on: [push, pull_request]
-env:
-  CI: true
 
 jobs:
   test:
@@ -26,10 +25,9 @@ jobs:
         uses: actions/checkout@v2
 
       - name: Set up Python
-        uses: actions/setup-python@v1
+        uses: actions/setup-python@v2
         with:
           python-version: ${{ matrix.python }}
-          architecture: "x64"
 
       - run: python --version
       - run: pip --version