Merge topic 'sphinx-domain-parallel'

ac89f9ec86 Merge branch 'backport-3.26-sphinx-domain-parallel'
f546ebfecc Utilities/Sphinx: Fix parallel documentation builds
4e11859e0e Utilities/Sphinx: Fix parallel documentation builds for 3.26

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: technocolordreamcoder <j_grant5@u.pacific.edu>
Merge-request: !8575