[CMake] Disable use of FetchContent on LGTM

FetchContent was repeatedly failing during extraction with:
> error: RPC failed; HTTP 403 curl 22 The requested URL returned error: 403 Forbidden

.lgtm.yml

@@ -4,6 +4,6 @@ extraction:
   cpp:
     index:
       build_command:
-      - "cmake '-H.' -Bbuild -DCMAKE_BUILD_TYPE=Debug -DWZ_ENABLE_WARNINGS:BOOL=OFF\
+      - "cmake '-H.' -Bbuild -DCMAKE_BUILD_TYPE=Debug -DWZ_DISABLE_FETCHCONTENT_GIT_CLONE:BOOL=ON -DWZ_ENABLE_WARNINGS:BOOL=OFF\
         \ -G\"Ninja\""
       - "cmake --build build --target warzone2100"

lib/ivis_opengl/CMakeLists.txt

@@ -61,7 +61,7 @@ target_link_libraries(ivis-opengl PRIVATE framework PNG::PNG ${HARFBUZZ_LIBRARIE
 target_link_libraries(ivis-opengl PUBLIC glad)
 if(WZ_ENABLE_BACKEND_VULKAN)
 	find_package(VulkanHeaders 108) # minimum supported version of the Vulkan headers is 108
-	if(NOT VulkanHeaders_FOUND AND NOT ${CMAKE_VERSION} VERSION_LESS "3.11.0")
+	if((NOT VulkanHeaders_FOUND AND NOT ${CMAKE_VERSION} VERSION_LESS "3.11.0") AND (NOT WZ_DISABLE_FETCHCONTENT_GIT_CLONE))
 		# Fetch newer Vulkan headers (using FetchContent, which requires CMake 3.11+)
 		include(FetchContent)
 		FetchContent_Declare(