Merge pull request #32649 from rails/universal-ruby-version

Create a .ruby-version compatible with MRI/JRuby by default

railties/lib/rails/generators/rails/app/templates/ruby-version.tt

-<%= RUBY_VERSION -%>
+<%= "#{RUBY_ENGINE}-#{RUBY_ENGINE_VERSION}" -%>

railties/test/generators/app_generator_test.rb

@@ -851,7 +851,7 @@ def test_inclusion_of_ruby_version
       assert_match(/ruby '#{RUBY_VERSION}'/, content)
     end
     assert_file ".ruby-version" do |content|
-      assert_match(/#{RUBY_VERSION}/, content)
+      assert_match(/#{RUBY_ENGINE}-#{RUBY_ENGINE_VERSION}/, content)
     end
   end