Fix labels in paginated plots with renamed layout scale

[jkrumbiegel]

The previous reftest didn't catch this because it accidentally did a meaningless conversion (uppercasing letters that were already uppercase)

df = (;
    subject = [1, 1, 2, 2],
    group = ["A", "B", "A", "B"],
    x = 1:4,
    y = 5:8,
)

spec = data(df) * mapping(:x, :y, layout = (:subject, :group) => tuple) * visual(Scatter)
scls = scales(
    Layout = (;
        categories = [(1, "A") => "One A", (2, "A") => "Two A", (1, "B") => "One B", (2, "B") => "Two B"]
    )
)
draw(spec, scls)
draw(paginate(spec, scls, layout = 3), 1)

Before

After