non_floating_tabs: apply relative selected tab position to pinned tabs

In overflow mode Firefox will override that anyway so no need to exclude
all pinned tabs.

chrome/non_floating_sharp_tabs.css

@@ -69,7 +69,7 @@ See the above repository for updates as well as full license text. */
 }
 
 /* Selected tab needs to be relative so it gets drawn over nav-bar top "border" */
-.tabbrowser-tab:not([pinned])[selected]{
+.tabbrowser-tab[selected]{
   position: relative;
   z-index: 1;
 }