API publications default to "private" even when "public" is set

The below configuration for an API:
```
publications:
  - ref: openai-gpt-4o-api-to-getting-started
    portal_id: !ref ai-portal#id
    visibility: public
```
defaults to _visibility: private_ in Konnect:

<img width="1726" height="875" alt="Image" src="https://github.com/user-attachments/assets/7f2da247-8e13-4ae1-afbb-72732ee20320" />