remove tests for ubuntu 20.04

Author: mhill900

.github/workflows/ci.yml

@@ -8,7 +8,7 @@ jobs:
     strategy:
       matrix:
         os: [
-          'ubuntu-20.04', 'ubuntu-22.04', 'ubuntu-24.04',
+          'ubuntu-22.04', 'ubuntu-24.04',
           'macos-13', 'macos-14',
           'windows-2019', 'windows-2022'
         ]