readonly is ignored when properties are inherited through allOf

[renke0]

Describe the bug
The request validator mistakenly makes a requestBody property required, even if it is marked as readonly. This is achievable by using inheritance with allOf.

To Reproduce
Given the spec:

openapi: 3.0.1
info:
  version: 1.0.0
  title: test
paths:
  /cars:
    post:
      requestBody:
        content:
          "application/json":
            schema:
              $ref: "#/components/schemas/Car"
      responses:
        200:
          description: OK
components:
  schemas:
    Car:
      type: object
      required:
        - id
        - name
      allOf:
        - $ref: "#/components/schemas/CarPartial"
    CarPartial:
      type: object
      properties:
        id:
          type: string
          readOnly: true
        name:
          type: string

With validateRequests: true in the middleware configuration, and by posting a request to the path with this request body:

{
  "name": "Opel Corsa"
}

Will result in a validation error with the following message: request/body must have required property 'id'

Actual behavior
A validation error will be thrown, indicating the id field marked as readonly is required in the request body.

Expected behavior
The request should be considered valid and no errors should be thrown.

Examples and context
Refer to the snippet above.

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