De-deprecating Ubuntu 20.04

We had no warning and since Ruby removed all the existing packages, I'm adding this back so we can build it and host it ourselves

Author: stephenleemcfarland

.github/workflows/build.yml

@@ -10,7 +10,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ ubuntu-22.04, ubuntu-24.04, ubuntu-22.04-arm, ubuntu-24.04-arm, macos-13, macos-14 ]
+        os: [ ubuntu-20.04, ubuntu-22.04, ubuntu-24.04, ubuntu-22.04-arm, ubuntu-24.04-arm, macos-13, macos-14 ]
         ruby: [jruby-10.0.0.0]
     runs-on: ${{ matrix.os }}
     steps: