Test against Ruby 4.0 (#397)

Author: tagliala

.github/workflows/rubocop.yml

@@ -19,7 +19,7 @@ jobs:
     - name: Set up Ruby
       uses: ruby/setup-ruby@v1
       with:
-        ruby-version: '3.4'
+        ruby-version: '4.0'
         rubygems: latest
         bundler-cache: true
     - name: RuboCop

.github/workflows/ruby.yml

@@ -16,7 +16,7 @@ jobs:
 
     strategy:
       matrix:
-        ruby-version: ['3.0', '3.1', '3.2', '3.3', '3.4']
+        ruby-version: ['3.0', '3.1', '3.2', '3.3', '3.4', '4.0']
         gemfile: [rails_7.0, rails_7.1, rails_7.2, rails_8.0, rails_8.1]
         postgres-version: ['16']
         channel: ['stable']
@@ -74,6 +74,12 @@ jobs:
             gemfile: rails_8.1
           - ruby-version: '3.4'
             gemfile: rails_7.0
+          - ruby-version: '4.0'
+            gemfile: rails_7.0
+          - ruby-version: '4.0'
+            gemfile: rails_7.1
+          - ruby-version: '4.0'
+            gemfile: rails_7.2
     env:
       BUNDLE_GEMFILE: gemfiles/${{ matrix.gemfile }}.gemfile
       TEST_CONFIG: ./spec/config.github.yml