Fix broken initialization arguments on TruffleRuby

The `make_synchronized_on_rbx` method is used to intercept the `.new`
method on Array/Hash/Set but it broke whenever the `.new` was being used
with arguments.

(This was shown by the Array/Hash/Set specs that were added in the
previous commits being broken on TruffleRuby.)

Author: ivoanjo

lib/concurrent/thread_safe/util/array_hash_rbx.rb

@@ -10,10 +10,9 @@ def _mon_initialize
             @_monitor = Monitor.new unless @_monitor # avoid double initialisation
           end
 
-          def self.new
-            obj = super
-            obj.send(:_mon_initialize)
-            obj
+          def initialize(*args)
+            _mon_initialize
+            super
           end
         end