[BE][Ez]: Use NotADirectoryError in tensorboard writer (#126534)

Slightly improve exception typing for tensorboard wrriter
Pull Request resolved: #126534
Approved by: https://github.com/ezyang

torch/utils/tensorboard/writer.py

@@ -916,7 +916,7 @@ def add_embedding(
                     "warning: Embedding dir exists, did you set global_step for add_embedding()?"
                 )
             else:
-                raise FileExistsError(
+                raise NotADirectoryError(
                     f"Path: `{save_path}` exists, but is a file. Cannot proceed."
                 )
         else: