Avoid race condition when expiring artifacts

## What does this MR do?

It may happen that job which purpose is to remove expired artifacts will be executed asynchronously when, in the meantime, project associated with given build gets removed by another async job. In that case we should not remove artifacts because such build will be eventually removed anyway along with artifacts, when project removal is complete.

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing

## What are the relevant issue numbers?

Closes #22296

See merge request !6881