Ignore libxml2 warning about already imported schemas
Ignore libxml2 warning about already imported schemas

This makes output from validation easier to read and less clogged.

mpreisler/openscap,jan-cerny/openscap,jan-cerny/openscap,postfix/openscap,isimluk/openscap,jan-cerny/openscap,redhatrises/openscap,jan-cerny/openscap,postfix/openscap,isimluk/openscap,openprivacy/openscap,OpenSCAP/openscap,mpreisler/openscap,isimluk/openscap,ybznek/openscap,postfix/openscap,OpenSCAP/openscap,redhatrises/openscap,redhatrises/openscap,mpreisler/openscap,openprivacy/openscap,openprivacy/openscap,redhatrises/openscap,isimluk/openscap,postfix/openscap,postfix/openscap,redhatrises/openscap,openprivacy/openscap,isimluk/openscap,ybznek/openscap,Hexadorsimal/openscap,mpreisler/openscap,ybznek/openscap,OpenSCAP/openscap,postfix/openscap,OpenSCAP/openscap,ybznek/openscap,jan-cerny/openscap,mpreisler/openscap,OpenSCAP/openscap,Hexadorsimal/openscap,ybznek/openscap,redhatrises/openscap,Hexadorsimal/openscap,Hexadorsimal/openscap,ybznek/openscap,mpreisler/openscap,openprivacy/openscap,Hexadorsimal/openscap,OpenSCAP/openscap,openprivacy/openscap,Hexadorsimal/openscap,isimluk/openscap,jan-cerny/openscap