unittest: fix no pickle

[lexdene]

the old NoPickle can be pickled since Python 3.11.
raise error in __getstate__ to fail pickle.

on Python 3.10:

Python 3.10.7 (main, Oct 12 2022, 15:33:27) [GCC 9.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import pickle
>>> class OldNoPickle(object):
...     def __getattr__(self, name):
...         pass
... 
>>> v1 = OldNoPickle()
>>> pickle.dumps(v1, 2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'NoneType' object is not callable
>>> class NoPickle(object):
...     def __getattr__(self, name):
...         pass
...     def __getstate__(self):
...         raise Exception('can not be pickled')
... 
>>> v2 = NoPickle()
>>> pickle.dumps(v2, 2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 5, in __getstate__
Exception: can not be pickled

on Python 3.11:

Python 3.11.1 (main, Jan 16 2023, 17:53:09) [GCC 9.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import pickle
>>> class OldNoPickle(object):
...     def __getattr__(self, name):
...         pass
... 
>>> v1 = OldNoPickle()
>>> pickle.dumps(v1, 2)
b'\x80\x02c__main__\nOldNoPickle\nq\x00)\x81q\x01.'
>>> class NoPickle(object):
...     def __getattr__(self, name):
...         pass
...     def __getstate__(self):
...         raise Exception('can not be pickled')
... 
>>> v2 = NoPickle()
>>> pickle.dumps(v2, 2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 5, in __getstate__
Exception: can not be pickled