test: Update cmake_using_source_directly to avoid libvulkan1 dependency

This is a similar problem to the one that volk's CMakeLists.txt used to have,
and was fixed in 3f3e0cb; this test will use
linked-in libvulkan1 without the change which isn't really how volk is designed
to be used.

Author: zeux

test/cmake_using_source_directly/CMakeLists.txt

@@ -33,7 +33,8 @@ endif()
 # Get Vulkan dependency
 find_package(Vulkan QUIET)
 if(TARGET Vulkan::Vulkan)
-  target_link_libraries(volk_test PRIVATE Vulkan::Vulkan)
+  # Note: We don't use target_link_libraries for Vulkan::Vulkan to avoid a static dependency on libvulkan1
+  target_include_directories(volk_test PRIVATE ${Vulkan_INCLUDE_DIRS})
 elseif(DEFINED ENV{VULKAN_SDK})
   target_include_directories(volk_test PRIVATE "$ENV{VULKAN_SDK}/include")
 endif()