bin/get-pick-list.sh: use test instead of [ ]

Latter is rather picky wrt surrounding white space. The explicit `test`
doesn't have that problem, plus the statements read a bit easier.

Cc: mesa-stable@lists.freedesktop.org
Reviewed-by: Juan A. Suarez <jasuarez@igalia.com>
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
(cherry picked from commit c0012a07)