[skip ci] Fix bug where checkmark was removed after the user dropdown was opened

app/assets/javascripts/users_select.js

@@ -357,9 +357,15 @@ import eventHub from './sidebar/event_hub';
               const $el = $(e.currentTarget);
               $el.find('.is-active').removeClass('is-active');
 
-              const initialSelected = getSelected().forEach((selectedId) => {
-                $el.find(`li[data-user-id="${selectedId}"] .dropdown-menu-user-link`).addClass('is-active');
-              });
+              function highlightSelected(id) {
+                $el.find(`li[data-user-id="${id}"] .dropdown-menu-user-link`).addClass('is-active');
+              }
+
+              if ($selectbox[0]) {
+                getSelected().forEach((selectedId) => highlightSelected(selectedId));
+              } else {
+                highlightSelected(selectedId);
+              }
             },
             updateLabel: $dropdown.data('dropdown-title'),
             renderRow: function(user) {