text: Title: Make contributor's checklist pass on CPython 3.12
  Body: At the time of writing, there are a couple of failures:
  * One line is missing coverage due to `async` optimizations in 3.12:
    `falcon/testing/client.py                  388      1    112      0    99%   2130`.
  * Sphinx seems to have some issues with 3.12 (`module 'configparser' has no attribute 'SafeConfigParser'`).