Exercise comparability test with LazyAttributeSet

LazyAttributeSet was added at rails#39612 for performance reason, it should
not break comparability with AttributeSet, which was added at 9e25e0e.

Author: kamipo

activemodel/test/cases/attribute_set_test.rb

@@ -274,9 +274,12 @@ def builder.build_from_database(values = {}, additional_types = {})
       attributes = builder.build_from_database(foo: "1", bar: "2")
       attributes2 = builder.build_from_database(foo: "1", bar: "2")
       attributes3 = builder.build_from_database(foo: "2", bar: "2")
+      attributes4 = attributes.deep_dup
 
       assert_equal attributes, attributes2
       assert_not_equal attributes2, attributes3
+      assert_equal attributes, attributes4
+      assert_equal attributes4, attributes
     end
 
     test "==(other) is safe to use with any instance" do