Add an apply Rails/EnumSyntax rubocop rule

This rule was added in rubocop-rails 2.26.0. Applying it allows
us to anticipate the deprecation of the current enum syntax
using keyword arguments, which is set to be removed in Rails
8.0, as mentioned in the rule's own documentation:

https://docs.rubocop.org/rubocop-rails/cops_rails.html#railsenumsyntax

.rubocop.yml

@@ -388,6 +388,9 @@ Rails/DynamicFindBy:
     - find_by_slug_or_id!
     - find_by_manager_login
 
+Rails/EnumSyntax:
+  Enabled: true
+
 Rails/EnumUniqueness:
   Enabled: true