I have no idea if itch.io has that kind of option, but since that warning specifically says the link gets flagged because it's not associated with the creator of the current page (aka you), maybe there is a way to flag it as an official cooperation. Never seen that warning before. (Also now I wonder if it also flags the links many adult game devs make to other games by other devs on the pages of their own games. Itch seems to have implemented a bunch of new warnings lately that don't all work to creators' benefits.)
EDIT: I just tested that and it seem linking a game of a different dev on your own game page doesn't get flagged. Tested with the link to From the Sin by Vorpal on the page of Succubus Kingdom by Cibbon. So maybe that warning only appears for links to other creators on your profile?