Fix z-index for project settings dropdown

What does this MR do?

It fixes the z-index value for the dropdown so that it does not appear behind other elements.

Why was this MR needed?

To fix the display of the dropdown.

Screenshots (if relevant)

See issue #28697 (closed).

Does this MR meet the acceptance criteria?

• Tests
  • Added for this feature/bug
  • All builds are passing
• Changelog entry added
• 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?

Closes #28697 (closed)