dim: reuse pull request signature for drm-intel-testing mails

I think adding a new config for this would be overkill, and this is
bound to be more correct than "Cheers, Daniel".

Leave the generic "Hi all" salute in place though.

Reviewed-by: Sean Paul <seanpaul@chromium.org>
Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>