docs/dev-tools: fix a broken URL in dev-tools/coccinelle.rst

docs/dev-tools: fix a broken URL in dev-tools/coccinelle.rst

The original supplemental documentation for coccicheck is
https://bottest.wiki.kernel.org/coccicheck, which redirects to a not found page,
thus change it to https://bottest.wiki.kernel.org/coccicheck.html,
which adds a suffix to original URL to make it direct to the right page.

Signed-off-by: LIU Haoyang <tttturtleruss@gmail.com>
Reviewed-by: Dongliang Mu <dzm91@hust.edu.cn>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <20260308100851.341-1-tttturtleruss@gmail.com>