Fix typo in api-reference.md: OpenAPI -> OpenAI (#23373)

## Description

It appears that there is a typo on the DMR API [documentation
page](https://docs.docker.com/ai/model-runner/api-reference/):
The section with **OpenAI**-compatible endpoints is named 'Available
**OpenAPI** endpoints'.

## Related issues or tickets:

No related issues or tickets found.

## Reviews

- [ ] Editorial review

Author: Renset

content/manuals/ai/model-runner/api-reference.md

@@ -66,9 +66,9 @@ on how you run Docker:
   DELETE /models/{namespace}/{name}
   ```
 
-### Available OpenAPI endpoints
+### Available OpenAI endpoints
 
-DMR supports the following OpenAPI endpoints:
+DMR supports the following OpenAI endpoints:
 
 - [List models](https://platform.openai.com/docs/api-reference/models/list):
 
@@ -189,4 +189,4 @@ curl --unix-socket $HOME/.docker/run/docker.sock \
             }
         ]
     }'
-```
+```