Resolve "Pin should show up at 1280px min"

What does this MR do?

Decreased window min width for pinned sidebar

What are the relevant issue numbers?

Closes #19171 (closed)
Part of #19200 (closed)

Screenshots (if relevant)

app/assets/javascripts/application.js.coffee

@@ -261,7 +261,7 @@ $ ->
   new Aside()
 
   # Sidenav pinning
-  if $window.width() < 1440 and $.cookie('pin_nav') is 'true'
+  if $window.width() < 1280 and $.cookie('pin_nav') is 'true'
     $.cookie('pin_nav', 'false', { path: '/' })
     $('.page-with-sidebar')
       .toggleClass('page-sidebar-collapsed page-sidebar-expanded')