Use class.allocate instead of #set_class

Author: eregon

src/main/ruby/core/exception.rb

@@ -391,8 +391,7 @@ def self.new(*args)
         end
       end
 
-      error = allocate
-      Truffle::Internal::Unsafe.set_class error, self
+      error = self.allocate
       Truffle.privately { error.initialize(*args) }
       error
     end