Merge pull request #28239 from y-yagi/use_appropriate_type_for_test_framework_option

Use appropriate type for `test_framework` option

railties/lib/rails/generators.rb

@@ -63,7 +63,7 @@ module Generators
         stylesheet_engine: :css,
         scaffold_stylesheet: true,
         system_tests: nil,
-        test_framework: false,
+        test_framework: nil,
         template_engine: :erb
       }
     }