Use each_pair in ActiveModel::AttributeAssignment#_assign_attributes

`ActiveModel::AttributeAssignment#assign_attributes` checks if the argument
responds to `each_pair`, and raises an exception if it does not.

However, in `_assign_attributes`, the argument is enumerated using `each`.
As a result, if the argument has `each_pair` but not `each`,
this error check results in a false negative.
(An example of such an object is `OpenStruct`.)

Author: kyanagi

activemodel/lib/active_model/attribute_assignment.rb

@@ -59,7 +59,7 @@ def attribute_writer_missing(name, value)
 
     private
       def _assign_attributes(attributes)
-        attributes.each do |k, v|
+        attributes.each_pair do |k, v|
           _assign_attribute(k, v)
         end
       end

activemodel/test/cases/attribute_assignment_test.rb

@@ -148,4 +148,14 @@ def attribute_writer_missing(name, value) = @assigned_attributes[name] = value
     model = Model.new
     assert_nil model.assign_attributes(ProtectedParams.new({}))
   end
+
+  test "passing an object with each_pair but without each" do
+    model = Model.new
+    h = { name: "hello", description: "world" }
+    h.instance_eval { undef :each }
+    model.assign_attributes(h)
+
+    assert_equal "hello", model.name
+    assert_equal "world", model.description
+  end
 end