Fixed label resetting when sorting by weight

What does this MR do?

Fixes a regression where sorting an issue by weight after filtering by label removes the label filter.

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

Look at testing for this kind of issue

Why was this MR needed?

To fix an issue

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

gitlab-org/gitlab-ce#30352