Update GHA for ubuntu-20.04 removal

Author: WardBrian

.github/workflows/testing.yml

@@ -21,7 +21,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-20.04]
+        os: [ubuntu-24.04]
         python-version: [3.8]
       fail-fast: false
     steps: