Update repo to isort v5 (#6686)

* Run new isort

* More changes

* Update CI, CONTRIBUTING and benchmarks

tests/test_modeling_encoder_decoder.py

@@ -27,18 +27,19 @@ from .test_modeling_roberta import RobertaModelTester
 
 
 if is_torch_available():
-    from transformers import (
-        BertModel,
-        BertLMHeadModel,
-        GPT2LMHeadModel,
-        RobertaModel,
-        RobertaForCausalLM,
-        EncoderDecoderModel,
-        EncoderDecoderConfig,
-    )
     import numpy as np
     import torch
 
+    from transformers import (
+        BertLMHeadModel,
+        BertModel,
+        EncoderDecoderConfig,
+        EncoderDecoderModel,
+        GPT2LMHeadModel,
+        RobertaForCausalLM,
+        RobertaModel,
+    )
+
 
 @require_torch
 class EncoderDecoderMixin: