documents: Make the document update tests individually idempotent
documents: Make the document update tests individually idempotent

Helps: bgo#633359

GNOME/libgdata,pwithnall/libgdata,Pecisk/libgdata-gtasks,Pecisk/libgdata-gtasks,Pecisk/libgdata,Distrotech/libgdata,Distrotech/libgdata,Pecisk/libgdata,Pecisk/libgdata-gtasks,Distrotech/libgdata,Pecisk/libgdata,pwithnall/libgdata