I do not know how the itch.io staff responds to clear license violations
Should you see such a clear violation, report it as a tos violoation. Of course it should be really clear and not guesswork. For your stuff you know what licenses apply. For stuff of other people you might be mistaken and then there is all those fair use things where it seems someone might be in violation of some things, but also might not be.
https://itch.io/docs/legal/terms#4-publisher-content
Publishers affirm, represent, and warrant that they own or have the rights, licenses, permissions and consents necessary to publish, duplicate, and distribute the submitted content.