Summary: Forms should have a label per https://dequeuniversity.com/rules/axe/4.10/link-select. This is not the case for the `<select>` element above the comment field which has "Add Action..." as its first option which is created via `id(new AphrontFormSelectControl())` in `PhabricatorApplicationTransactionCommentView`. Add an `aria-label` attribute for screenreader use. Ref T16072 Test Plan: * While logged in, go to http://phorge.localhost/T1 or http://phorge.localhost/D1 or http://phorge.localhost/P1 * Inspect the `<select>` element above the comment field (which has "Add Action..." as its first option) with and without this patch. * Optionally, run an Accessibility check in Chromium Lighthouse. Reviewers: O1 Blessed Committers, chris Reviewed By: O1 Blessed Committers, chris Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno Maniphest Tasks: T16072 Differential Revision: https://we.phorge.it/D26051