xref. https://github.com/github/accessibility-audits/issues/8568

Description

The problem was that when shift-tabbing from the co-authors input text, the focus would go into an item of the autocomplete list right before closing the autocomplete list, so the focused element would be immediately removed and focus would go to the body element.

This PR makes the list inside the autocomplete component not focusable with the Tab key, which prevents the focus from going into the list when shift-tabbing from the co-authors input text.

Given we are using aria-activedescendant to manage focus inside the autocomplete list, we keep the DOM focus in the input text. That means, "shift-tabbing" from that scenario should move the DOM focus to the "toggle co-authors" button and the DOM focus should never go to the autocomplete list.

Screenshots

Release notes

Notes: [Fixed] Fix logical tab order from co-authors text box