Run CI for Python 3.6 on Ubuntu 20.04

The now latest Ubuntu no longer ships with 3.6.

.github/workflows/python-package.yaml

@@ -5,7 +5,7 @@ on: [push, pull_request]
 jobs:
   test:
 
-    runs-on: ubuntu-latest
+    runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: false
       matrix:
@@ -15,6 +15,12 @@ jobs:
         - '3.8'
         - '3.9'
         - '3.10'
+        - '3.11'
+        - '3.12.0-alpha - 3.12.0'
+      include:
+        - os: "ubuntu-latest"
+        - os: "ubuntu-20.04"
+          python-version: "3.6"
 
     steps:
     - uses: actions/checkout@v3

tox.ini

@@ -16,6 +16,8 @@ python =
     3.8: py38
     3.9: py39
     3.10: py310
+    3.11: py311
+    3.12: py312
 
 [testenv:black]
 deps =