NetworkManager->Spawn info->Register Spawnable Prefabs should throw warning on adding prefab without Network Identity

1. What happened

2. How we can reproduce it using the example you attached
1 Create new project
2 Create Empty Object and add NetworkManager and go to Spawn info->Register Spawnable Prefabs
3 Press "+"
4 In project view create prefab without Network Identity and add this prefab to created in previous step slot - notice that the slot is still empty and there is no any error or warning

Actual result: NetworkManager->Spawn info->Register Spawnable Prefabs should throw warning on adding prefab without Network Identity, instead of silent ignore
- please see attached video