CI: Switch ubuntu-20.04 with ubuntu-22.04 runner (#82)

Author: glensc

.github/workflows/test.yml

@@ -14,12 +14,11 @@ on:
 
 jobs:
   test:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     name: Python ${{ matrix.python }}
     strategy:
       matrix:
         python:
-          - "3.6"
           - "3.7"
           - "3.8"
           - "3.9"