We should be lint-failing on $ref with siblings

[acunniffe]

Describe the bug
Optic is not failing when linting specs that have $ref and sibling properties specified:

field:
  $ref: ...
  type: object

The values are all getting merged. This happens at the dereference stage for some reason. The validation schema is working on a dereferenced spec, so it never sees a $ref.

Expected behavior
Should fail when linting

Not allowed in OpenAPI https://swagger.io/docs/specification/using-ref/

Screenshots
If applicable, add screenshots to help explain your problem.

Details (please complete the following information):

• OS and version: [e.g. Mac OS 13.1]
• Optic version: [e.g. v0.37.1]
• NodeJS version: [e.g. 18.0.0]

Additional context
Add any other context about the problem here.

[niclim]

Additionally, we should detect things like:

schema:
  type: object
  oneOf / allOf / anyOf:...

This will cause similar issues