use ubuntu 20.04 for legacy gh actions. no more python 2.7

Author: johanlundberg

.github/workflows/run-tests.yaml

@@ -8,10 +8,10 @@ on: [push, pull_request]
 jobs:
 
   unittests_legacy:
-    runs-on: ubuntu-22.04
+    runs-on: ubuntu-20.04
     strategy:
       matrix:
-        python-version: ["2.7", "3.6"]
+        python-version: ["3.6"]
 
     steps:
       - uses: actions/checkout@v3
@@ -39,7 +39,7 @@ jobs:
     runs-on: ubuntu-22.04
     strategy:
       matrix:
-        python-version: ["3.9", "3.10"]
+        python-version: ["3.9", "3.10", "3.11", "3.12"]
 
     steps:
       - uses: actions/checkout@v3