Fix new navigation wrapping caret and increasing height

What does this MR do?

Fix new navigation wrapping caret and increasing height by removing the "Activity" item sooner hidden-md.

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

• Are we okay with hiding the "Activity" item sooner, hidden-md?
  • Should we instead hide the search bar sooner?

Why was this MR needed?

Previously from 1003px to 991px when the hidden-sm breakpoint kicks in, the dropdown caret would wrap to the next line and make the nav bar too tall.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

Closes #36821 (closed)