### Check for existing issues

- [x] I have searched the existing issues and checked that my issue is not a duplicate.

### What happened?

When attempting to create a new credential for RunwayML through the LiteLLM UI, the credential form behaves differently from other providers.

After selecting RunwayML from the Provider dropdown:

The API Key field disappears. The API Base field disappears. It becomes impossible to enter the required connection parameters. Submitting the form results in a 422 Unprocessable Content response.

Image: ghcr.io/berriai/litellm-database:main-stable

### Steps to Reproduce

1. Login to LiteLLM UI. 2. Navigate to Credentials. 3. Click Add Credential. 4. Select RunwayML in the Provider dropdown. 5. Observe that the API Key and API Base fields disappear. 6. Attempt to save the credential.

### Relevant log output

```shell INFO: 172.22.0.1:39072 - "GET /public/providers/fields HTTP/1.1" 200 OK

INFO: 172.22.0.1:35292 - "GET /ui/assets/logos/runwayml.png HTTP/1.1" 404 Not Found

INFO: 172.22.0.1:35292 - "GET /ui/assets/logos/runwayml.png HTTP/1.1" 404 Not Found

INFO: 172.22.0.1:37276 - "POST /credentials HTTP/1.1" 422 Unprocessable Conten…