AdjustmentReason: Add :dependent option

We should not delete adjustment reasons if there are adjustments created
with them.

Author: mamhoff

.rubocop_todo.yml

@@ -1,6 +1,6 @@
 # This configuration was generated by
 # `rubocop --auto-gen-config`
-# on 2025-06-26 11:28:28 UTC using RuboCop version 1.76.0.
+# on 2025-07-08 12:12:57 UTC using RuboCop version 1.76.0.
 # The point is for the user to remove these configuration records
 # one by one as the offenses are removed from the code base.
 # Note that changes in the inspected code, or installation of new
@@ -332,7 +332,7 @@ Rails/FilePath:
     - "core/lib/spree/testing_support/dummy_app.rb"
     - "sample/lib/spree/sample.rb"
 
-# Offense count: 43
+# Offense count: 42
 # Configuration parameters: Include.
 # Include: **/app/models/**/*.rb
 Rails/HasManyOrHasOneDependent:

core/app/models/spree/adjustment_reason.rb

@@ -2,7 +2,7 @@
 
 module Spree
   class AdjustmentReason < Spree::Base
-    has_many :adjustments, inverse_of: :adjustment_reason
+    has_many :adjustments, inverse_of: :adjustment_reason, dependent: :restrict_with_error
 
     validates :name, presence: true, uniqueness: { case_sensitive: false, allow_blank: true }
     validates :code, presence: true, uniqueness: { case_sensitive: false, allow_blank: true }