Integrate gitlab-ci/allow-check-job-to-fail and 1 more

--

Commit: seco-ne/yocto/infrastructure/gitlab-ci@ad9d367e

Allow check job to fail

This makes merging a project MR possible even if the manifest has
received new commits since the MR pipeline build has run. The developer
is responsible for deciding whether it is safe to merge it without
having a build based on the latest manifest.

BCS 746-000794

--

Commit: seco-ne/yocto/infrastructure/gitlab-ci@81c2ad85

merge_into_manifest: fix error message if MR already exists