Resolve "Inconsistency: Repo Title "down caret" cropped on smaller viewports"

What does this MR do?

Fixes an issue where the dropdown chevron for a project list was not visible on smaller viewports.

This MR also changes the dropdown trigger into a button element for better accessibility (it can now be tabbed to like any link).

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

None that I can think of.

Why was this MR needed?

Better accessibility and support for smaller viewports.

Screenshots (if relevant)

Dropdown toggle now targetable by pressing tab to select.

Chevron no longer hidden when project title length triggers overflow: ellipsis.

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• Tests
  • All builds are passing
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #21506 (closed)