CI: Drop EOL Ruby versions, add Ruby 3.4

Author: olleolleolle

.github/workflows/main.yml

@@ -11,15 +11,15 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: [ '3.0', '3.1', '3.2', '3.3' ]
+        ruby: [ '3.2', '3.3', '3.4' ]
         rails: [ '6.1', '7.0' ]
 
     name: Ruby ${{ matrix.ruby }} / Rails ${{ matrix.rails }}
     env:
       BUNDLE_GEMFILE: gemfiles/Gemfile-activemodel-${{ matrix.rails }}.x
 
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v6
 
     - name: Setup Ruby
       uses: ruby/setup-ruby@v1