Drop EOL Ubuntu 20.04 from Linux wheel builds

Author: swt2c

.github/workflows/build-linux-wheels.yml

@@ -60,7 +60,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ ubuntu-20.04, ubuntu-22.04, ubuntu-24.04 ]
+        os: [ ubuntu-22.04, ubuntu-24.04 ]
         python-version: [ '3.9', '3.10', '3.11', '3.12', '3.13', '3.14' ]
         architecture: [ 'x64' ]