js: declare variable for email domain hint div (#45984)

src/authentic2/static/authentic2/js/email_domains_suggestions.js

@@ -67,6 +67,7 @@ String.prototype.similarity = function(string) {
 }
 
 $(function() {
+  var $domain_hint_div;
   $('input[type=email]').on('change', function() {
     var $email_input = $(this);
     var suggested_domains = $(this).data('suggested-domains').split(':');