Fix `GitAccess` spec once again.

- In 5b92c54319cd0e10f879a35bf6aab85a8e04e540, we destroyed all the
  default access levels for a factory-created protected branch.

- Inadvertently, we also destroyed all spec-created access levels,
  leading to a number of failures, which should now be fixed.

spec/factories/protected_branches.rb

@@ -14,9 +14,9 @@ FactoryGirl.define do
     end
 
     trait :remove_default_access_levels do
-      after(:create) do |protected_branch|
-        protected_branch.push_access_levels.destroy_all
-        protected_branch.merge_access_levels.destroy_all
+      after(:build) do |protected_branch|
+        protected_branch.push_access_levels = []
+        protected_branch.merge_access_levels = []
       end
     end