Explicitly state that we're trying to prepend twice

spec/lib/gitlab/patch/prependable_spec.rb

@@ -76,9 +76,8 @@ describe Gitlab::Patch::Prependable do
                 ce.const_get(:ClassMethods)])
     end
 
-    it 'prepends only once' do
+    it 'prepends only once even if called twice' do
-      ce.prepend(ee)
+      2.times { ce.prepend(ee) }
-      ce.prepend(ee)
 
       subject