ci: update Ubuntu runner to 24.04 LTS

Author: mshibuya

.github/workflows/test.yml

@@ -39,7 +39,7 @@ jobs:
           - ruby: jruby-head
             gemfile: gemfiles/rails-7-0.gemfile
             experimental: false
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-24.04
     continue-on-error: ${{ matrix.experimental }}
     env:
       BUNDLE_GEMFILE: ${{ matrix.gemfile }}
@@ -66,7 +66,7 @@ jobs:
 
   rubocop:
     name: RuboCop
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-24.04
     steps:
       - uses: actions/checkout@v4
       - name: Set up Ruby