ImportError: cannot import name 'NoReturn' - during pip install --upgrade with Python 3.6.1

[emezh]

Description

After pip upgrade to 21.1 (Py 3.6.1) any pip install command fails with
ImportError: cannot import name 'NoReturn'

upgrading to pip==21.0.1 works fine.

Expected behavior

no error thrown

pip version

21.1

Python version

3.6.1

OS

CentOS 7.1

How to Reproduce

$ /tools/python/3.6.1-RHEL7/bin/python3 -m venv --copies venv_py3
$ source venv_py3/bin/activate
(venv_py3) $ pip3 install --upgrade pip
Cache entry deserialization failed, entry ignored
Collecting pip
  Downloading https://files.pythonhosted.org/packages/ac/cf/0cc542fc93de2f3b9b53cb979c7d1118cffb93204afb46299a9f858e113f/pip-21.1-py3-none-any.whl (1.5MB)
    100% |████████████████████████████████| 1.6MB 1.1MB/s 
Installing collected packages: pip
  Found existing installation: pip 9.0.1
    Uninstalling pip-9.0.1:
      Successfully uninstalled pip-9.0.1
Successfully installed pip-21.1

(venv_py3) $ pip3 install -r requirements.txt
Traceback (most recent call last):
  File "venv_py3/bin/pip3", line 7, in <module>
    from pip._internal.cli.main import main
  File "venv_py3/lib/python3.6/site-packages/pip/_internal/cli/main.py", line 9, in <module>
    from pip._internal.cli.autocompletion import autocomplete
  File "venv_py3/lib/python3.6/site-packages/pip/_internal/cli/autocompletion.py", line 10, in <module>
    from pip._internal.cli.main_parser import create_main_parser
  File "venv_py3/lib/python3.6/site-packages/pip/_internal/cli/main_parser.py", line 8, in <module>
    from pip._internal.cli import cmdoptions
  File "venv_py3/lib/python3.6/site-packages/pip/_internal/cli/cmdoptions.py", line 30, in <module>
    from pip._internal.utils.hashes import STRONG_HASHES
  File "venv_py3/lib/python3.6/site-packages/pip/_internal/utils/hashes.py", line 2, in <module>
    from typing import TYPE_CHECKING, BinaryIO, Dict, Iterator, List, NoReturn
ImportError: cannot import name 'NoReturn'

Output

No response

Code of Conduct

• I agree to follow the PSF Code of Conduct.

[pfmoore]

This is fixed in master and will be in the 21.1.1 release (no confirmed date for that yet). See #9831.