Integrate gitlab-ci/allow_failure

Commit: seco-ne/yocto/infrastructure/gitlab-ci@6656c465

CI: allow failure in new jobs 'handle_artifacts' and 'report-image-diff'

It seems that these jobs are not yet completly errorsafe and we could ignore the failure without changing the build artifacts.

Source merge request: seco-ne/yocto/infrastructure/gitlab-ci!394 (merged)

mentioned in merge request seco-ne/yocto/infrastructure/gitlab-ci!394 (merged)

merged