Replace Python 3.6 with 3.11 in CI

Author: a-hurst

.github/workflows/run_tests.yml

@@ -22,7 +22,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ['2.7', '3.6', '3.7', '3.8', '3.9', '3.10']
+        python-version: ['2.7', '3.7', '3.8', '3.9', '3.10', '3.11']
         sdl2: ['2.26.0']
         name-prefix: ['Linux (Python ']
         include: