Update CI to newer runner

Ubuntu 20.04 image on GitHub Actions will be deprecated on 2025-04-01.

Author: Matoking

.github/workflows/tests.yml

@@ -9,7 +9,7 @@ permissions: read-all
 
 jobs:
   test:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     strategy:
       matrix:
         python-version: ['3.6', '3.7', '3.8', '3.9', '3.10', '3.11', '3.12']