Fix group wiki feature specs

These need `stub_group_wikis` to show group wikis at all, let alone the
empty state.

ee/spec/features/groups/wiki/user_views_wiki_empty_spec.rb

@@ -3,10 +3,16 @@
 require 'spec_helper'
 
 RSpec.describe 'Group > User views empty wiki' do
+  include WikiHelpers
+
   let_it_be(:user) { create(:user) }
 
   let(:wiki) { create(:group_wiki, group: group) }
 
+  before do
+    stub_group_wikis(true)
+  end
+
   it_behaves_like 'User views empty wiki' do
     context 'when group is public' do
       let(:group) { create(:group, :public) }

ee/spec/features/groups/wikis_spec.rb

@@ -3,11 +3,14 @@
 require "spec_helper"
 
 RSpec.describe 'Group wikis' do
+  include WikiHelpers
+
   let_it_be(:user) { create(:user) }
 
   let(:wiki) { create(:group_wiki, user: user) }
 
   before do
+    stub_group_wikis(true)
     wiki.container.add_owner(user)
   end