[tutorials][ML] Fix wrong file name in tutorial index.

Currently the Higgs Classification ML tutorial is in the wrong section due to a typo in the file name.

Author: Jonah Ascoli

tutorials/machine_learning/index.md

@@ -137,6 +137,6 @@
 | ml_dataloader_NumPy.py | Loading batches of events from a ROOT dataset as Python generators of numpy arrays. |
 | ml_dataloader_PyTorch.py | Loading batches of events from a ROOT dataset into a basic PyTorch workflow. |
 | ml_dataloader_TensorFlow.py | Loading batches of events from a ROOT dataset into a basic TensorFlow workflow. |
-| ml_dataloader_Higgs_Classification | Loading batches of events from different files for a data-normalization workflow. |
+| ml_dataloader_Higgs_Classification.py | Loading batches of events from different files for a data-normalization workflow. |
 | ml_dataloader_resampling.py | Loading batches of events from an imbalanced ROOT dataset and balancing them. |