CI: Run `reuse lint` across the tree

Signed-off-by: Simon McVittie <smcv@collabora.com>
7 jobs for wip/reuse in 9 minutes and 3 seconds (queued for 3 seconds)
Status Name Job ID Coverage
  Test
manual build:arch #101544
allowed to fail manual
passed build:asan #101540

00:03:35

passed build:bionic #101543

00:08:26

passed build:buster #101542

00:08:12

passed build:stretch #101541

00:09:03

passed build:ubsan #101539

00:03:31

passed reuse #101545

00:02:11