WIP: try running in containers

Author: nattylinden

.github/workflows/ci.yaml

@@ -9,14 +9,16 @@ on:
 jobs:
   build:
     name: Test & Build
+    container:
+      image: python:${{ matrix.python-version }}
+    env:
+      PYTHON: ${{ matrix.python-version }}
+    runs-on: ubuntu-latest
     strategy:
       # Finish the other builds even if one fails.
       fail-fast: false
       matrix:
         python-version: ['2.7', '3.7', '3.8', '3.10']
-    runs-on: [ubuntu-20.04]
-    env:
-      PYTHON: ${{ matrix.python-version }}
     steps:
       - uses: actions/checkout@v3
         with: