Cannot set OpenAPI version

[TimonVS]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the bug has not already been reported

Fastify version

3.29.0

Plugin version

6.0.1

Node.js version

16.14.2

Operating system

macOS

Operating system version (i.e. 20.04, 11.3, 10)

12.2.1

Description

The openapi option accepts an object of the type OpenAPIV3.Document, which includes an openapi property to set the OpenAPI version.
fastify-swagger doesn't seem to pick this up, as the openapi version stays at the default value of 3.0.3.

Steps to Reproduce

await app.register(fastifySwagger, {
  routePrefix: '/documentation',
  openapi: {
    openapi: '3.1.0', // <--- This is allowed in the TypeScript interface, but is not reflected in the generated OpenAPI schema
    info: {
      title: 'Test swagger',
      description: 'Testing the Fastify swagger API',
      version: '0.1.0',
    },
  }
});

Expected Behavior

No response