ci: bump ci base distro to ubuntu 20.04

ubuntu-18.04 has been remove since a few and so tests are silently not
running.
So while at it update python versions tested, drop 2.7 and 3.5 and add
3.11.

.github/workflows/python.yml

@@ -9,11 +9,11 @@ on:
 jobs:
   build:
 
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-20.04
     strategy:
       max-parallel: 4
       matrix:
-        python-version: [2.7, 3.5, 3.6, 3.7, 3.8, 3.9, "3.10"]
+        python-version: [3.6, 3.7, 3.8, 3.9, "3.10", "3.11"]
 
     steps:
     - uses: actions/checkout@v2

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 envlist =
-	py{310,39,38,37,36,35,27},
+	py{311,310,39,38,37,36},
 	coverage-report
 
 [testenv]
@@ -19,4 +19,4 @@ skip_install = true
 setenv = COVERAGE_FILE=.coverage
 commands =
     coverage combine
-    coverage report
+    coverage report