admin-guide: Fix list formatting in tained-kernels.html

Without this patch, the points 1-9 in the list are rendered as an HTML
blockquote containing a list, causing them to be indented further than
the rest of the list.

While at it, also fix the quotation marks around G and P.

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>