a11y: Set aria-label attribute for Edit button on workboard card

Summary:
Links should have a discernible name per https://dequeuniversity.com/rules/axe/4.10/link-name
The "Edit" buttons (created by creating `id(new PHUIListItemView())` in `ProjectBoardTaskCard`) for each task card on a project workboard currently do not have any description what they actually do (they have a tooltip already but that is not recognized by screenreader software).

This is quite similar to rP60c0ed86.

Refs T16072

Test Plan:
* While logged in, go to http://phorge.localhost/project/board/1/
* Hover over a task card in a column to see the Edit button in the upper right corner. It now has a descriptive `aria-label="Edit Task"` attribute.
* Optionally, run an Accessibility check in Chromium Lighthouse.

Reviewers: O1 Blessed Committers, mainframe98

Reviewed By: O1 Blessed Committers, mainframe98

Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest Tasks: T16072

Differential Revision: https://we.phorge.it/D26223