style(utility): do not check the type of "__getattr__" in "AttrsMixin"

Mypy does not raise an error on a `missing method` when base class
defines a `__getattr__` function, so make mypy ignore that method
by decorating `__getattr__` with `typing.no_type_check`.

related issue: python/mypy#6251

tensorbay/utility/attr.py

@@ -11,7 +11,18 @@
 
 """
 
-from typing import Any, Callable, Dict, List, Optional, Tuple, TypeVar, Union
+from typing import (
+    Any,
+    Callable,
+    Dict,
+    List,
+    NoReturn,
+    Optional,
+    Tuple,
+    TypeVar,
+    Union,
+    no_type_check,
+)
 
 from typing_extensions import Protocol
 
@@ -65,7 +76,7 @@ def __init__(
         if error_message:
             self.error_message = error_message
 
-    def __getattr__(self, name: str) -> None:
+    def __getattr__(self, name: str) -> NoReturn:
         raise AttributeError(
             _DEFAULT_ERROR_MESSAGE.format(class_name=self.__class__.__name__, attr_name=name)
         )
@@ -123,7 +134,8 @@ def __eq__(self, other: object) -> bool:
 
         return self.__dict__ == other.__dict__
 
-    def __getattr__(self, name: str) -> None:
+    @no_type_check
+    def __getattr__(self, name: str) -> NoReturn:
         """Raise an AttributeError exception when an attr does not exist.
 
         Arguments: