While introducing latest malcontent in the toolbox, mistakenly wrong
path to install-meson-project.sh was used. Correct this by using the
proper path, after copying the script there.
Moreover, disable building documentation in malcontent subproject
libgsystemservice, so that we don't have to install more dependencies.
Fixes: b7992b80 ("ci: Include latest malcontent in the toolbox")
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3873>