Make the second argument to `attribute` optional

While working on updating Paper Trail for 5.1 compatibility, I noticed
that I was required to pass a second argument to `attribute`. I didn't
intend for this to be the case, as `attribute :foo` is totally
reasonable shorthand for "I want `attr_accessor :foo`, but also have it
work with things like `.attributes` and `ActiveRecord::Dirty`"

activerecord/CHANGELOG.md

+*   Change the type argument of `ActiveRecord::Base#attribute` to be optional.
+    The default is now `ActiveRecord::Type::Value.new`, which provides no type
+    casting behavior.
+
+    *Sean Griffin*
+
 *   Fix that unsigned with zerofill is treated as signed.
 
     Fixes #27125.

activerecord/lib/active_record/attributes.rb

@@ -191,7 +191,7 @@ module ClassMethods
       # tracking is performed. The methods +changed?+ and +changed_in_place?+
       # will be called from ActiveModel::Dirty. See the documentation for those
       # methods in ActiveModel::Type::Value for more details.
-      def attribute(name, cast_type, **options)
+      def attribute(name, cast_type = Type::Value.new, **options)
         name = name.to_s
         reload_schema_from_cache
 

activerecord/test/cases/attributes_test.rb

@@ -255,5 +255,13 @@ def deserialize(*)
 
       assert_includes inspection, "non_existent_decimal"
     end
+
+    test "attributes do not require a type" do
+      klass = Class.new(OverloadedType) do
+        attribute :no_type
+      end
+      assert_equal 1, klass.new(no_type: 1).no_type
+      assert_equal "foo", klass.new(no_type: "foo").no_type
+    end
   end
 end