Charliecloud not compatible with sphinx-rtd_theme 3.0.0
The get_html_theme_path() from sphinx_rtd_theme now raises a warning with the latest version making docs builds of Charliecloud fail.
Upstream commit: https://github.com/readthedocs/sphinx_rtd_theme/pull/1576/commits/cc5067af431abbc32f2601945f5cc6d1a543d67f
Justification: https://github.com/readthedocs/sphinx_rtd_theme/pull/1479#issuecomment-2296317034