chore: fix type issue (#429)

Author: taoche

backend/modules/model_gateway/model_gateway.py

@@ -121,7 +121,7 @@ def _register_models(self, provider_config: ModelProviderConfig):
                 -> Added to self.llm_models
 
             3. Reranking model:
-                name: "openai/rerank-english-v2.0"
+                name: "cohere/rerank-english-v2.0"
                 type: ModelType.reranking
                 -> Added to self.reranker_models