tests: Mark a conditional rendering test as buggy on llvmpipe.

Similarly to RADV, this is a kind of perverted situation: in principle Vulkan doesn't allow vkCmdResolveImage() to be executed conditionally (i.e., it is unaffected by conditional execution), which means that vkd3d cannot implement conditional rendering for ResolveSubresource(), hence the todo. However, like RADV, llvmpipe apparently violates the specification and still executes the image resolution command conditionally. So that's a llvmpipe bug, even if one that helps us doing the right thing.