Remove support for Ubuntu 20.04 in CI and build workflows

Signed-off-by: Tsuyoshi Hombashi <tsuyoshi.hombashi@gmail.com>

Author: thombashi

.github/workflows/build_and_release.yml

@@ -27,7 +27,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-20.04, ubuntu-22.04, ubuntu-24.04]
+        os: [ubuntu-22.04, ubuntu-24.04]
 
     steps:
       - uses: actions/checkout@v4
@@ -121,11 +121,6 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - uses: actions/download-artifact@v4
-        with:
-          name: binaries-ubuntu-20.04
-          path: ${{ env.DIST_DIR_NAME }}
-
       - uses: actions/download-artifact@v4
         with:
           name: binaries-ubuntu-22.04

.github/workflows/ci.yml

@@ -105,7 +105,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-20.04, ubuntu-22.04, ubuntu-24.04]
+        os: [ubuntu-22.04, ubuntu-24.04]
     concurrency:
       group: ${{ github.event_name }}-${{ github.workflow }}-installer-${{ matrix.os }}
       cancel-in-progress: true