fix: use proper X-Api-Key header format when docling api key provided (open-webui#20652)

Author: kaileywong

backend/open_webui/retrieval/loaders/main.py

@@ -143,7 +143,7 @@ def load(self) -> list[Document]:
         with open(self.file_path, "rb") as f:
             headers = {}
             if self.api_key:
-                headers["X-Api-Key"] = f"Bearer {self.api_key}"
+                headers["X-Api-Key"] = f"{self.api_key}"
 
             r = requests.post(
                 f"{self.url}/v1/convert/file",