CLDC-3766: Ensure copy for Q78 is found correctly

app/models/form/sales/questions/staircase.rb

@@ -2,7 +2,7 @@ class Form::Sales::Questions::Staircase < ::Form::Question
   def initialize(id, hsh, page)
     super
     @id = "staircase"
-    @copy_key = "sales.#{page.subsection.id}.staircasing"
+    @copy_key = "sales.#{page.subsection.copy_key}.staircasing"
     @type = "radio"
     @question_number = QUESTION_NUMBER_FROM_YEAR[form.start_date.year] || QUESTION_NUMBER_FROM_YEAR[QUESTION_NUMBER_FROM_YEAR.keys.max]
   end

app/models/form/sales/subsections/shared_ownership_scheme.rb

@@ -4,6 +4,7 @@ class Form::Sales::Subsections::SharedOwnershipScheme < ::Form::Subsection
     @id = "shared_ownership_scheme"
     @label = "Shared ownership scheme"
     @depends_on = [{ "ownershipsch" => 1, "setup_completed?" => true }]
+    @copy_key = "sale_information"
   end
 
   def pages

app/models/form/subsection.rb

@@ -14,6 +14,10 @@ class Form::Subsection
 
   delegate :form, to: :section
 
+  def copy_key
+    @copy_key ||= @id
+  end
+
   def questions
     @questions ||= pages.flat_map(&:questions)
   end