gitlab-ci: Keep capturing bundles as artifacts for hawkBit

Commit 0f98e2a4 "gitlab-ci: Try to upload artifacts immediately" was a bit too eager to skip capturing all OSTree bundles when in fact we still need to capture the main update bundles to upload them to hawkBit.

Putting the hawkBit upload directly in the job building the bundles would be a better option, but it seems too early since the hawkBit upload has been restored only recently and it may still be flaky, so a dedicated jobw with allow_failure: true still seems appropriate.