purl-next: Create new JSON schema for PURL tests

[pombredanne]

We need to create a new JSON schema for PURL tests

[pombredanne]

This has been merged with:

• Refine Purl type schema package-url/purl-spec#514

The new schema is at:

• https://github.com/package-url/purl-spec/blob/main/schemas/purl-test.schema.json