Resolve "Admin Settings: Cannot read property 'addEventListener' of null"

app/assets/javascripts/pages/admin/application_settings/show/index.js

+import initUserInternalRegexPlaceholder from '../../application_settings/account_and_limits';
+
+document.addEventListener('DOMContentLoaded', initUserInternalRegexPlaceholder());

app/assets/javascripts/pages/admin/index.js

 import initAdmin from './admin';
-import initUserInternalRegexPlaceholder from './application_settings/account_and_limits';
-document.addEventListener('DOMContentLoaded', () => {
-  initAdmin();
-  initUserInternalRegexPlaceholder();
-});
+document.addEventListener('DOMContentLoaded', initAdmin());

changelogs/unreleased/56622-admin-settings-cannot-read-property-addeventlistener-of-null.yml

+---
+title: Load initUserInternalRegexPlaceholder only when required
+merge_request: 24522
+author:
+type: fixed

spec/javascripts/test_bundle.js

@@ -187,6 +187,7 @@ if (process.env.BABEL_ENV === 'coverage') {
     './terminal/terminal_bundle.js',
     './users/users_bundle.js',
     './issue_show/index.js',
+    './pages/admin/application_settings/show/index.js',
   ];
   describe('Uncovered files', function() {