Documentation: kunit: fix trivial typo

Missing closing block-quote

Signed-off-by: Tales Aparecida <tales.aparecida@gmail.com>
Reviewed-by: David Gow <davidgow@google.com>
Reviewed-by: Sadiya Kazi <sadiyakazi@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>