Switch to new ActiveRecord enum args, not deprecated in Rails 7.2

Rails 7.2 says:
```
DEPRECATION WARNING: Defining enums with keyword arguments is deprecated and will be removed
in Rails 8.0. Positional arguments should be used instead:

enum :kithe_model_type, {:collection=>0, :work=>1, :asset=>2}
```

app/models/kithe/model.rb

@@ -23,7 +23,7 @@ class Kithe::Model < ActiveRecord::Base
   #
   # Since the rails enum uses an int field, this doens't take up too much extra
   # space in pg or anything, and is convenient.
-  enum kithe_model_type: { collection: 0, work: 1, asset: 2}
+  enum :kithe_model_type, { collection: 0, work: 1, asset: 2}
 
   attr_json_config(default_accepts_nested_attributes: { reject_if: :all_blank })