Backends: SDL3: fixes use of now removed SDL_bool.

backends/imgui_impl_sdl3.cpp

@@ -1104,7 +1104,7 @@ static int ImGui_ImplSDL3_CreateVkSurface(ImGuiViewport* viewport, ImU64 vk_inst
 {
     ImGui_ImplSDL3_ViewportData* vd = (ImGui_ImplSDL3_ViewportData*)viewport->PlatformUserData;
     (void)vk_allocator;
-    SDL_bool ret = SDL_Vulkan_CreateSurface(vd->Window, (VkInstance)vk_instance, (VkAllocationCallbacks*)vk_allocator, (VkSurfaceKHR*)out_vk_surface);
+    bool ret = SDL_Vulkan_CreateSurface(vd->Window, (VkInstance)vk_instance, (VkAllocationCallbacks*)vk_allocator, (VkSurfaceKHR*)out_vk_surface);
     return ret ? 0 : 1; // ret ? VK_SUCCESS : VK_NOT_READY
 }