ci: use ubuntu-22.04 runner for python 3.9 testing

GitHub doesn't offer ubuntu-20.04 runners since april 2025

Signed-off-by: Benjamin Cabé <[email protected]>

Author: kartben

.github/workflows/test.yml

@@ -33,7 +33,7 @@ jobs:
         # Python 3.9
         - python: '3.9'
           os: Linux
-          builder: ubuntu-20.04
+          builder: ubuntu-22.04
         - python: '3.9'
           os: macOS
           builder: macos-13