Fix copy file to folder (#4075)

Author: Wauplin

src/huggingface_hub/hf_api.py

@@ -12617,7 +12617,7 @@ def copy_files(self, source: str, destination: str, *, token: str | bool | None
 
         destination_bucket_id = destination_handle.bucket_id
         destination_path = destination_handle.path
-        if destination_path == "":
+        if destination_path == "" or destination.endswith("/"):
             destination_is_directory = True
         else:
             # Check if destination path is an existing file or a directory in the bucket