Merge topic 'backport-sphinx-file-encoding' into release-3.26

e4f26edc1c Tests: Always load presets schema as UTF-8
fc2b60ca6b Sphinx: Modernize UTF-8 encoding handling when updating CMake.qhp
853f069103 Sphinx: Specify encoding when opening files for title extraction

Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !8521