Support allOf sibling property required

[Swiftwork]

OpenAPI 3.1 supports sibling properties to allOf. It would be very useful if the following schema was supported by the codegen. Now it just ignores the required property.

User:
  required:
    - id
    - firstName
  allOf:
    - type: object
      properties:
        id:
          type: string
    - $ref: '#/components/schemas/UserProperties'

Resolved by https://github.com/deepmap/oapi-codegen/pull/717