- There are some flash banners which do not
  have a close el ([example][1]) but our
  function expected `getCloseEl` to exist.
- This MR fixes a bug that'll prevent a lot of
  JavaScript from working since we try to
  set up flashes in our critical application path
  ([see comment][2]).

[1]: ee/app/views/layouts/header/_read_only_banner.html.haml
[2]: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/61831#note_583912822

Changelog: fixed