Fix sentinel token IDs in data collator for Flax T5 pretraining script (#14477)

examples/flax/language-modeling/run_t5_mlm_flax.py

@@ -291,7 +291,7 @@ class FlaxDataCollatorForT5MLM:
         start_indices[:, 0] = mask_indices[:, 0]
 
         sentinel_ids = np.where(start_indices != 0, np.cumsum(start_indices, axis=-1), start_indices)
-        sentinel_ids = np.where(sentinel_ids != 0, (sentinel_ids + self.tokenizer.vocab_size - 1), 0)
+        sentinel_ids = np.where(sentinel_ids != 0, (len(self.tokenizer) - sentinel_ids), 0)
         sentinel_ids -= mask_indices - start_indices
 
         return sentinel_ids