Nullable properties have additional | null declaration in OpenAPI 3.1

[RinseV]

What are the steps to reproduce this issue?

1. Generate the type for a nullable property from an OpenAPI 3.1 schema:

openapi: 3.1.0
info:
  title: Nullables
  description: 'OpenAPI 3.1 examples'
  version: 1.0.0
paths: {}
components:
  schemas:
    Test:
      properties:
        example_nullable:
          type:
            - string
            - 'null'
      title: Test
      type: object

What happens?

The type is generated as follows:

export interface Test {
  example_nullable?: TestExampleNullable;
}

export type TestExampleNullable = string | null | null;

What were you expecting to happen?

Type type is generated as follows:

export type TestExampleNullable = string | null;

Any logs, error output, etc?

N/A

Any other comments?

This is due to this PR that now also checks whether a null type is included in the array of types. However, with the OpenAPI 3.1 specification, nullable properties are declared by adding the null type to the type array in the property, rather than specifying nullable: true. As such, the nullable variable is now true for the property where it was false before. I'm not entirely sure where the second | null is coming from however.

What versions are you using?

 System:
    OS: macOS 15.2
    CPU: (8) arm64 Apple M3
    Memory: 136.42 MB / 16.00 GB
    Shell: 5.9 - /bin/zsh
  npmPackages:
    @tanstack/react-query: ^5.63.0 => 5.63.0 
    @tanstack/vue-query: ^4.22.0 => 4.22.0 
    axios: ^0.26.1 => 0.26.1 
    msw: ^2.0.2 => 2.0.2 
    react: ^18.3.1 => 18.3.1 
    swr: ^2.2.4 => 2.2.4 
    vue: ^3.3.4 => 3.3.4 
    zod: ^3.23.8 => 3.23.8

I'm using Orval 7.4.1, but this issue was introduced in 7.4.0.