Fixed testvulkan on macOS (thanks @proton991!)

Fixes https://github.com/libsdl-org/SDL/issues/10351

test/testvulkan.c

@@ -228,6 +228,9 @@ static void createInstance(void)
     appInfo.apiVersion = VK_API_VERSION_1_0;
     instanceCreateInfo.sType = VK_STRUCTURE_TYPE_INSTANCE_CREATE_INFO;
     instanceCreateInfo.pApplicationInfo = &appInfo;
+#ifdef __APPLE__
+    instanceCreateInfo.flags = VK_INSTANCE_CREATE_ENUMERATE_PORTABILITY_BIT_KHR;
+#endif
 
     instanceCreateInfo.ppEnabledExtensionNames = SDL_Vulkan_GetInstanceExtensions(&instanceCreateInfo.enabledExtensionCount);
     result = vkCreateInstance(&instanceCreateInfo, NULL, &vulkanContext->instance);
@@ -445,6 +448,9 @@ static void createDevice(void)
     VkDeviceCreateInfo deviceCreateInfo = { 0 };
     static const char *const deviceExtensionNames[] = {
         VK_KHR_SWAPCHAIN_EXTENSION_NAME,
+#ifdef __APPLE__        
+        "VK_KHR_portability_subset"
+#endif        
     };
     VkResult result;