message: Update squash-and-merge title when PR title changes
diff: import select from 'select-dom';
  import features from '../libs/features';
  +import observeEl from '../libs/simplified-element-observer';
  +
  +function updateSquashAndMergeTitle() {
  + const title = select('.js-issue-title').textContent;
  + const number = select('.gh-header-number').textContent;
  + select<HTMLTextAreaElement>('#merge_title_field').value = `${title.trim()} (${number})`;
  +}
  function init() {
  const btn = select('.merge-message .btn-group-squash [type=button]');
  @@ -7,11 +14,8 @@ function init() {
  return false;
  }
  - btn.addEventListener('click', () => {
  - const title = select('.js-issue-title').textContent;
  - const number = select('.gh-header-number').textContent;
  - select<HTMLTextAreaElement>('#merge_title_field').value = `${title.trim()} (${number})`;
  - });
  + btn.addEventListener('click', updateSquashAndMergeTitle);
  + observeEl('.js-issue-title', updateSquashAndMergeTitle);
  }
  features.add({
  