[a11y] donation banner has two main concerns

[CharlesNepote]

The donation banner is displayed only with a mouse click: <span id="hide-donate-banner" class="material-icons" onclick="DonationButton();">close</span>.

The analyzer we use reports two main issues:

1. The mouse event attribute doesn't have a keyboard equivalent: see https://www.w3.org/WAI/WCAG21/Techniques/client-side-script/SCR20
2. The element is a forced user interface control without the proper role attribute: see https://www.w3.org/WAI/WCAG21/Techniques/failures/F59

For the first one, it should be possible to open it thanks to keyboard. The solution seems to only add a keyboard event:

<span id="hide-donate-banner" class="material-icons" onclick="DonationButton();" onkeypress="DonationButton();" role="button">close</span>

The second one is about giving a role to the span, or better replace it by a button tag.