gitlab-ci: apt upgrade so that tests run with current updates

The MD5 signature stuff was failing in tests because the CI image was
using a quite old version of Java's jarsigner, which had not yet disabled
MD5.
2 jobs for archive-policy-fix in 30 minutes and 41 seconds (queued for 5 seconds)
Status Job ID Name Coverage
  Test
passed #20900157
metadata_v0

00:03:43

passed #20900153
test

00:30:40