Uninterned Symbol can be duped since ruby 2.4.1

https://github.com/ruby/ruby/commit/11e6bd5ac2a2eebfa589bd6db8c9c4daa337733e

Leaving the 2.4.0 conditional for now, in order never to forget backporting r57407 to 2.4.1

activesupport/test/core_ext/object/duplicable_test.rb

@@ -4,7 +4,10 @@
 require "active_support/core_ext/numeric/time"
 
 class DuplicableTest < ActiveSupport::TestCase
-  if RUBY_VERSION >= "2.4.0"
+  if RUBY_VERSION >= "2.4.1"
+    RAISE_DUP = [method(:puts), Complex(1), Rational(1)]
+    ALLOW_DUP = ["1", "symbol_from_string".to_sym, Object.new, /foo/, [], {}, Time.now, Class.new, Module.new, BigDecimal.new("4.56"), nil, false, true, 1, 2.3]
+  elsif RUBY_VERSION >= "2.4.0"  # Due to 2.4.0 bug. This elsif cannot be removed unless we drop 2.4.0 support...
     RAISE_DUP = [method(:puts), Complex(1), Rational(1), "symbol_from_string".to_sym]
     ALLOW_DUP = ["1", Object.new, /foo/, [], {}, Time.now, Class.new, Module.new, BigDecimal.new("4.56"), nil, false, true, 1, 2.3]
   else