ci: Work-around bug in meson
Work-around race in meson's gtk-doc support: FileNotFoundError: [Errno 2] No such file or directory: '/builds/GNOME/evince/_build/help/reference/libdocument/html/libevdocument.devhelp2' -> '/builds/GNOME/evince/_build/help/reference/libdocument/html/libevdocument-3.0.devhelp2'