spin-row: Fix accessible role

Widgets with role presentation can't have a label. Set the group role instead.

As it's theoretically possible to add prefix and suffix widgets to this row as well, we can't just hide it from a11y completely.

This slipped by me when I changed this the first time around.

To ensure we are still on the right track I've also tested it a bit and apart from some unrelated orca / focus bugs inside the text it seems to work well, and gtk does not show any more warnings.