Person game: Don't offer Wikisource items outside of Author namespaces

[Former user]

The person game is currently proposing many items out of the EN and PT Wikisources

These wikisources put Author pages in a dedicated namespace.

Any item with link only to those Wikisources, but outside of those namespaces, can be considered as Not a person.

Note: this policy exists for most Wikisources instances, but not all.