Follow-up from "Conditionally render create group buttons"

The following discussion from !63871 (merged) should be addressed:

• @pslaughter started a discussion: (+1 comment)

  question (non-blocking): Is it possible that we want to do a permission check on this one too? This also comes from app/views/layouts/nav/projects_dropdown/_show.html.haml.

  We can handle this either here or in a follow-up. Your call 😄

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Notes and observations:

• Auditor users can create projects/groups. This is intentional.

• External users are not able to create a project.
  This is reflected in the dropdown:
  
  However, this is not reflected in the Projects menu:
  \

  Similarly, in the new :combined_menu, this is also available:
  

To address this, I'll likely add the current_user.can_create_project? check to the relevant code