Deprecate orders/could_not_transition view

api/app/views/spree/api/orders/could_not_transition.json.jbuilder

@@ -1,4 +1,9 @@
 # frozen_string_literal: true
 
+Spree::Deprecation.warn(
+  'spree/api/orders/could_not_transition is deprecated.' \
+  ' Please use spree/api/errors/could_not_transition'
+)
+
 json.error(I18n.t(:could_not_transition, scope: "spree.api.order"))
 json.errors(@order.errors.to_hash)

api/spec/views/spree/api/orders/could_not_transition.json.jbuilder_spec.rb

@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+require "spec_helper"
+
+RSpec.describe 'spree/api/orders/could_not_transition.json.jbuilder' do
+  helper(Spree::Api::ApiHelpers)
+
+  let(:template_deprecation_error) do
+    'spree/api/orders/could_not_transition is deprecated.' \
+    ' Please use spree/api/errors/could_not_transition'
+  end
+
+  it 'shows a deprecation error' do
+    assign(:order, instance_double(Spree::Order, errors: {}))
+
+    expect(Spree::Deprecation).to receive(:warn).with(template_deprecation_error)
+
+    render
+  end
+end