Fix typo showing error message after destroy page

Changelog: fixed

app/controllers/concerns/wiki_actions.rb

@@ -177,7 +177,7 @@ module WikiActions
       redirect_to wiki_path(wiki),
       status: :found
     else
-      @error = response
+      @error = response.message
       render 'shared/wikis/edit'
     end
   end

spec/support/shared_examples/controllers/wiki_actions_shared_examples.rb

@@ -486,7 +486,7 @@ RSpec.shared_examples 'wiki controller actions' do
           end.not_to change { wiki.list_pages.size }
 
           expect(response).to render_template('shared/wikis/edit')
-          expect(assigns(:error).message).to eq('Could not delete wiki page')
+          expect(assigns(:error)).to eq('Could not delete wiki page')
         end
       end
     end