Fix: unpin flake8 and fix cs errors (#4367)

* Fix: unpin flake8 and fix cs errors

* Ok we still need to quote those

tests/test_tokenization_common.py

@@ -19,11 +19,21 @@ import pickle
 import shutil
 import tempfile
 from collections import OrderedDict
-from typing import Dict, Tuple, Union
+from typing import TYPE_CHECKING, Dict, Tuple, Union
 
 from tests.utils import require_tf, require_torch
 
 
+if TYPE_CHECKING:
+    from transformers import (
+        PretrainedConfig,
+        PreTrainedTokenizer,
+        PreTrainedTokenizerFast,
+        PreTrainedModel,
+        TFPreTrainedModel,
+    )
+
+
 def merge_model_tokenizer_mappings(
     model_mapping: Dict["PretrainedConfig", Union["PreTrainedModel", "TFPreTrainedModel"]],
     tokenizer_mapping: Dict["PretrainedConfig", Tuple["PreTrainedTokenizer", "PreTrainedTokenizerFast"]],