tests: Update doc validation
tests: Update doc validation

Print a single warning line identifying the number of missing tests.

elongbug/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,Radamanthe/VulkanSamples,KhronosGroup/Vulkan-LoaderAndValidationLayers,critsec/Vulkan-LoaderAndValidationLayers,elongbug/Vulkan-LoaderAndValidationLayers,Radamanthe/VulkanSamples,critsec/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,critsec/Vulkan-LoaderAndValidationLayers,Radamanthe/VulkanSamples,elongbug/Vulkan-LoaderAndValidationLayers,Radamanthe/VulkanSamples,elongbug/Vulkan-LoaderAndValidationLayers,Radamanthe/VulkanSamples,Radamanthe/VulkanSamples,critsec/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers