Rework how we display loading of the new PR dropdown
    
    This reworks the display of the new-pr dropdown,
    so we show loading animations for both the async
    requests, and display the results in a consistent manner.
    
    Previously, whatever request finished first, those results
    would be at the top.
    
    This does not change the ordering of the results, just how
    the dropdown is displayed.
    
    Fixes: #3812