[13.0] Tier validation subtype of messages

[CasVissers-360ERP]

def _notify_accepted_reviews(self):
def _notify_rejected_review(self):

both these methods use subtype="mt_comment" which I think is incorrect.

In for example a purchase order workflow we don't want to send a message to the supplier of the PO (which also follower) if a PO is internally rejected or approved.

I suggest I create a PR to change the subtype to mt_note.

@LoisRForgeFlow

[LoisRForgeFlow]

I fully agree, could you open a PR addressing it?