tests: Fix UnusedPreserveAttachment
tests: Fix UnusedPreserveAttachment

Undefined shouldn't be an error since its a valid enumerant.

Change-Id: I542b47cdf885bd9ccb96a0a113a56a849423800a

KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools