BRD-20938 remove Ubuntu 20.04 testing it's no longer supported on github

Author: jamesh-gomo

.github/workflows/build.yml

@@ -37,7 +37,6 @@ jobs:
           # Latest Ubuntu is currently 24.04, which doesn't support older versions of Ruby. We need to decide what versions of Ruby need to be tested against.
           # - ubuntu-latest # currently ubuntu-22.04
           - ubuntu-22.04
-          - ubuntu-20.04
           - macos-latest # currently macos-14, ARM based
           - macos-latest-large # currently macos-14 Intel based
           - macos-13