Example markup for errors and validation out of date

[edwardhorsford]

The example markup on the errors and validation page still has separate headings and legends - which was changed in #507

[kr8n3r]

@selfthinker could you update the page with the code change in your PR?

[edwardhorsford]

I think this may be a mistake on my part.

The example which I thought was a single question isn't our standard format - as it has a heading, some text, and then the legend.

The example is probably correct, but we're missing an example of a page-per-thing validation pattern which is likely the most common page. I'll raise an issue for that instead.