fix: skip duplicated api-reference slug

Author: Andrew Jiang

fern/docs.yml

@@ -1,3 +1,5 @@
+# yaml-language-server: $schema=https://schema.buildwithfern.dev/docs-yml.json
+
 instances:
   - url: https://vapi.docs.buildwithfern.com
     custom-domain: docs.vapi.ai
@@ -340,6 +342,7 @@ navigation:
       - api: API Reference
         api-name: api
         flattened: true
+        skip-slug: true
         paginated: true
         snippets: 
           typescript: "@vapi/server-sdk"