Drop ubuntu-20.04 support

Author: dalance

.github/workflows/build.yml

@@ -12,7 +12,6 @@ jobs:
         os:
           - { image: ubuntu-24.04, name: linux }
           - { image: ubuntu-22.04, name: linux }
-          - { image: ubuntu-20.04, name: linux }
     runs-on: ${{ matrix.os.image }}
     env:
       CI_BUILD_STAGE_NAME: build