fix: prevent new window when shift-clicking links in split view glance, b=closes https://github.com/zen-browser/desktop/issues/11409, p=#11424

Co-authored-by: Nihal <121309701+nihalxkumar@users.noreply.github.com>

src/browser/themes/shared/preferences/zen-preferences.css

@@ -559,6 +559,7 @@ groupbox h2 {
 #helpButton,
 #support-firefox,
 #tabGroupSuggestions,
+#web-appearance-manage-themes-link,
 .mission-message {
   display: none !important;
 }