I've not come across this specifically mentioned ... and usually judge mine ... 'just tight and a tiny bit more' so I don't damage the washer or sump. As long as there's no leak of oil that's tight enough in my book!
Out of interest I've looked at the technical manual and, whilst I can't see the sump plug specifically mentioned, all other bolts relating to the sump are as per the attached. Note this 0.9 is in m-kg. [And for comparison the cylinder head bolts, for example, have a 3.2 m-kg torque figure].