Rails5 fix AttachmentRegistryFinder arel queries

What does this MR do?

Similar problem as in gitlab-ce!19796 and gitlab-ce!18330 where the query was the query has something like uploads.model_id IN (0) in Rails 5 due to a bug.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

rails5 upgrade

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Conform by the code review guidelines
  • Has been reviewed by a Backend maintainer
  • Has been reviewed by a Database specialist
• EE specific content should be in the top level /ee folder
• Conform by the merge request performance guides
• Conform by the style guides
• Conform by the database guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Closes #6742 (closed) Closes #6745 (closed) Closes #6743 (closed)