Replace error by warning when loading an architecture in another (#11207)

* Replace error by warning when loading an architecture in another

* Style

* Style again

* Add a test

* Adapt old test

tests/test_modeling_bert_generation.py

@@ -231,13 +231,7 @@ class BertGenerationEncoderTester:
         self.parent.assertEqual(result.logits.shape, (self.batch_size, self.seq_length, self.vocab_size))
 
     def prepare_config_and_inputs_for_common(self):
-        config_and_inputs = self.prepare_config_and_inputs()
-        (
-            config,
-            input_ids,
-            input_mask,
-            token_labels,
-        ) = config_and_inputs
+        config, input_ids, input_mask, token_labels = self.prepare_config_and_inputs()
         inputs_dict = {"input_ids": input_ids, "attention_mask": input_mask}
         return config, inputs_dict
 
@@ -259,6 +253,11 @@ class BertGenerationEncoderTest(ModelTesterMixin, GenerationTesterMixin, unittes
         config_and_inputs = self.model_tester.prepare_config_and_inputs()
         self.model_tester.create_and_check_model(*config_and_inputs)
 
+    def test_model_as_bert(self):
+        config, input_ids, input_mask, token_labels = self.model_tester.prepare_config_and_inputs()
+        config.model_type = "bert"
+        self.model_tester.create_and_check_model(config, input_ids, input_mask, token_labels)
+
     def test_model_as_decoder(self):
         config_and_inputs = self.model_tester.prepare_config_and_inputs_for_decoder()
         self.model_tester.create_and_check_model_as_decoder(*config_and_inputs)