[accessibility] Collapsed attribution button should have discernible text

[jnapolitan]

Hi team,

It seems as though when rendering the collapsed attribution button, the <span> nested within the button has an appropriate title attribute applied to it, but the <button> itself does not. This does not meet WCAG and will fail when running Lighthouse/Axe.

mapbox-gl-js version: 3.2.0

browser: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/123.0.0.0 Safari/537.36

Steps to Trigger Behavior

1. Load the map at a screen width that renders the collapsed attribution button
2. Run Lighthouse/Axe devtools, or inspect the element to see the <button> element doesn't have discernible text