Update test matrix

.github/workflows/build.yml

@@ -12,7 +12,6 @@ on:
 
 jobs:
   test:
-    runs-on: ubuntu-latest
     strategy:
       matrix:
         python-version:
@@ -21,6 +20,15 @@ jobs:
           - 3.8
           - 3.9
           - "3.10"
+          - "3.11"
+        include:
+          - os: ubuntu-latest
+
+          # older versions need older OS
+          - python-version: 3.6
+            os: ubuntu-20.04
+
+    runs-on: ${{ matrix.os }}
 
     steps:
       - uses: actions/checkout@v2