CI: switch to Ubuntu 22.04

Author: dmgav

.github/workflows/testing.yml

@@ -5,7 +5,7 @@ on: [push, pull_request]
 jobs:
   build:
 
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     strategy:
       matrix:
         python-version: ["3.9", "3.10", "3.11", "3.12", "3.13"]