Remove ubuntu-20.04

Author: eregon

.github/workflows/build.yml

@@ -66,7 +66,7 @@ jobs:
       id: matrix
       with:
         script: |
-          const osList = ['ubuntu-20.04', 'ubuntu-22.04', 'ubuntu-24.04', 'ubuntu-22.04-arm', 'ubuntu-24.04-arm', 'macos-13', 'macos-14']
+          const osList = ['ubuntu-22.04', 'ubuntu-24.04', 'ubuntu-22.04-arm', 'ubuntu-24.04-arm', 'macos-13', 'macos-14']
           const asanHead = { os: 'ubuntu-24.04', name: 'asan' }
           const asan34   = { os: 'ubuntu-24.04', name: '3.4-asan' }
           const skipSlow = "${{ github.event_name == 'workflow_dispatch' && github.event.inputs.skip_slow == 'true' }}"