Deprecated usage of Document#getName() when displaying a category without a name

When a blog category has no name property value, displaying it (e.g. in the Categories panel) falls back to the deprecated com.xpn.xwiki.api.Document#getName() getter, which logs:

WARN o.a.v.introspection - Deprecated usage of getter [com.xpn.xwiki.api.Document.getName] in xwiki:Blog.CategoriesPanel@342,29

The call is in the #getCategoryName macro of Blog.CategoriesCode ($categoryDoc.name). It should use $categoryDoc.documentReference.name instead.

This warning also makes BlogManagementTest fail on CI (forbidden log content), see https://ci.xwiki.org/job/XWiki%20Contrib/job/application-blog/job/master/525/