Set correct JSON schema for manifest.json and package.json

When working with Unity packages, Rider will set the schema for manifest.json to ["foxx-manifest"](https://github.com/SchemaStore/schemastore/blob/master/src/schemas/json/foxx-manifest.json) via the [schemastore.org catalog](https://github.com/SchemaStore/schemastore/blob/8427c3f9c279586e4f8a8a1bd3ee5e262eeca963/src/api/json/catalog.json#L50-L55). It appears to set the schema for `package.json` internally.

Make sure these files are using the correct schema.