fix train_new_from_iterator in the case of byte-level tokenizers (#17549)

tests/models/roberta/test_modeling_roberta.py

@@ -112,6 +112,11 @@ class RobertaModelTester:
             initializer_range=self.initializer_range,
         )
 
+    def get_pipeline_config(self):
+        config = self.get_config()
+        config.vocab_size = 300
+        return config
+
     def prepare_config_and_inputs_for_decoder(self):
         (
             config,