Since this introduces a new metadata type we'll need to generate a new json schema. To do that you'll need to:

• Head to https://github.com/anchore/syft/blob/main/internal/constants.go#L9 and bump the json schema version from 3.2.1 to 3.2.3 (we use schema-ver rules for selecting next versions, and this is a new, non-breaking addition to the schema... see https://github.com/anchore/syft/blob/main/schema/json/README.md#versioning).
• from the root of the repo run make generate-json-schema

This will create a new json schema file with the right version.

I was not able to reproduce this issue locally, is there some kind of cache I need to clear?

Diff of latest json schema to the changes in this PR (helpful for other reviewers):

diff schema-3.2.1.json schema-3.2.2.json
164a165,186
>     "DartPubMetadata": {
>       "required": [
>         "name",
>         "version"
>       ],
>       "properties": {
>         "name": {
>           "type": "string"
>         },
>         "version": {
>           "type": "string"
>         },
>         "hosted_url": {
>           "type": "string"
>         },
>         "vcs_url": {
>           "type": "string"
>         }
>       },
>       "additionalProperties": true,
>       "type": "object"
>     },
665a688,690
>               "$ref": "#/definitions/DartPubMetadata"
>             },
>             {

I force pushed to rebase + fix the merge conflict I caused with the readme update.