Merge topic 'flake8-sphinx'

adbc8c982d Utilities/Sphinx: Fix flake8 gripes in cmake.py
9fab1ad504 Utilities/Sphinx: Use f-strings in cmake.py
cef51925a4 Utilities/Sphinx: Require Sphinx 2.x or later

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: Alex <leha-bot@yandex.ru>
Merge-request: !8324