ci: Add verification step for generated source
ci: Add verification step for generated source

This check ensures that the committed generated source files match the
output of the committed generators. We used to have this check on
TravisCI, but it must have gotten lost in the transition to GitHub
Actions.

Change-Id: If6a27994b3bfe8dbd09a962d90cc0c528489bd93

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