Fix football doughnut labelling

By using bonzo's attr method

Fixes https://github.com/guardian/frontend/issues/5787 and https://github.com/guardian/frontend/issues/5785
Ah I see, I was confused as we weren't using the class methods - it's not just the `classList` but `className` too.
[Here's a little fix](https://github.com/component/classes/pull/3/files) - but pretty sure Bonzo won't add it for compatibility.