drm/doc: Fix title underline for "Task information"

drm/doc: Fix title underline for "Task information"

Fix the following warning:

Documentation/gpu/drm-uapi.rst:450: WARNING: Title underline too short.

Task information
--------------- [docutils]

Fixes: cd37124b4093 ("drm/doc: Add a section about "Task information" for the wedge API")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Closes: https://lore.kernel.org/lkml/20250618150333.5ded99a0@canb.auug.org.au/
Reviewed-by: Raag Jadav <raag.jadav@intel.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Bagas Sanjaya <bagasdotme@gmail.com>
Link: https://lore.kernel.org/r/20250704190724.1159416-1-andrealmeid@igalia.com
Signed-off-by: André Almeida <andrealmeid@igalia.com>