Try to fix CI.

Author: gpx1000

attachments/advanced_gltf/CMake/FindVulkanHpp.cmake

@@ -0,0 +1,14 @@
+# FindVulkanHpp.cmake — re-entrancy shim
+#
+# advanced_gltf/CMakeLists.txt calls find_package(VulkanHpp) before
+# add_subdirectory(simple_engine), and simple_engine/CMakeLists.txt calls it
+# again.  simple_engine's implementation uses FetchContent_Populate, which is
+# fatal when the content is already populated (cmake 3.x).  This shim is
+# found first (advanced_gltf/CMake precedes simple_engine/CMake in
+# CMAKE_MODULE_PATH) and short-circuits the second invocation.
+if(TARGET VulkanHpp::VulkanHpp)
+    set(VulkanHpp_FOUND TRUE)
+    return()
+endif()
+
+include("${CMAKE_CURRENT_LIST_DIR}/../../simple_engine/CMake/FindVulkanHpp.cmake")