"class:: toc-title" was a workaround for older Sphinx versions that are
no longer supported.

The canonical way to add a heading to the ToC is to use :caption:.
Do that.

Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: gaochao <gaochao49@huawei.com>
Cc: Yanteng Si <siyanteng@loongson.cn>
Cc: Wu XiangCheng <bobwxc@email.cn>
Cc: Fangrui Song <maskray@google.com>
Cc: Wan Jiabing <wanjiabing@vivo.com>
Cc: Alex Shi <alexs@kernel.org>
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20231027081830.195056-6-vegard.nossum@oracle.com