[csswg-drafts] [css-gcpm-3] page group example is incorrect (#3524)

faceless2 has just created a new issue for https://github.com/w3c/csswg-drafts:

== [css-gcpm-3] page group example is incorrect ==
https://drafts.csswg.org/css-gcpm-3/#document-page-selectors has this to say on page groups:
> When the page property is applied to an element that also has a forced break property applied, a page group is created.

But examples 13 and 14 immediately below that don't show a forced-break. Without this, neighbouring `div` elements with the same `page` attribute could be on the same page.

To fix example 13:
* Change `div { page: A }` to `div { page: A; break-before: page }`

To fix example 14:
* Change `div.Chapter { page: body; }` to `div.Chapter { page: body; break-before: page }`

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/3524 using your GitHub account