https://developercommunity.visualstudio.com/t/support-json-schema-draft-06-draft-07/796216
VS still doesn’t support draft 7 for json-schemes and is stuck at draft 4-5. Hence the warning.
It’s a false positive.
EDIT
Mike (see below) suggests a work around. Be sure to check it out and give Mike an upvote if it works (so that he’ll be the first answer listed).