Remove ubuntu-20.04

Author: eregon

.github/workflows/build.yml

@@ -78,7 +78,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ ubuntu-20.04, ubuntu-22.04, ubuntu-24.04, ubuntu-22.04-arm, ubuntu-24.04-arm, macos-13, macos-14 ]
+        os: [ ubuntu-22.04, ubuntu-24.04, ubuntu-22.04-arm, ubuntu-24.04-arm, macos-13, macos-14 ]
         name: [ '-head', '+graalvm-head' ]
     runs-on: ${{ matrix.os }}
     steps: