twisted.internet.cfreactor not importable on Python 3.8

[graingert]

Describe the incorrect behavior you saw
fails with:

src/twisted/internet/cfreactor.py:474:24: error: X | Y syntax for unions requires Python 3.10  [syntax]
        _currentSimulator: object | None = None

>>> import twisted.internet.cfreactor
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/graingert/projects/twisted/src/twisted/internet/cfreactor.py", line 92, in <module>
    class CFReactor(PosixReactorBase):
  File "/home/graingert/projects/twisted/src/twisted/internet/cfreactor.py", line 474, in CFReactor
    _currentSimulator: object | None = None
TypeError: unsupported operand type(s) for |: 'type' and 'NoneType'

Describe how to cause this behavior

import it on Python 3.8

Preferable a Short, Self Contained, Correct (Compilable), Example on a branch or on a gist.

Automated tests that are demonstrating the failure would be awesome.

Describe the correct behavior you'd like to see
no import error

Testing environment
N/A