fix(infinity/transformation.py): fix linting error

Author: krrishdholakia

Diff for: litellm/llms/infinity/rerank/transformation.py

@@ -20,13 +20,15 @@
 
 
 class InfinityRerankConfig(CohereRerankConfig):
-    def get_complete_url(self, api_base: str, model: str) -> str:
+    def get_complete_url(self, api_base: Optional[str], model: str) -> str:
+        if api_base is None:
+            raise ValueError("api_base is required for Infinity rerank")
         # Remove trailing slashes and ensure clean base URL
         api_base = api_base.rstrip("/")
         if not api_base.endswith("/rerank"):
             api_base = f"{api_base}/rerank"
         return api_base
-        
+
     def validate_environment(
         self,
         headers: dict,