Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

Following the directions for "Upload via Multipart Requests" here generates a method only taking one file, instead of an array.

openapi-generator version

current master, docker image hash sha256:8d1bc0ad57397450b9a8a004c5f1d7a512a5e370f3e54837122d44d3fbd5da4b

OpenAPI declaration file content or url

openapi: 3.0.3
info:
  title: bug example
  version: 0.0.1
paths:
  /example:
    post:
      requestBody:
        content:
          multipart/form-data:
            schema:
              type: object
              properties:
                filename:
                  type: array
                  items:
                    type: string
                    format: binary
      responses:
        '200':
          description: OK

Generation Details / Steps to reproduce

1. Save the above file as example.yml
2. Using docker-for-windows and git-bash, from the same folder as example.yml: MSYS_NO_PATHCONV=1 docker run --rm -v "${PWD}:/local" openapitools/openapi-generator-cli@sha256:8d1bc0ad57397450b9a8a004c5f1d7a512a5e370f3e54837122d44d3fbd5da4b generate --input-spec "/local/example.yml" --output "/local/example" --generator-name aspnetcore
3. cat example/src/Org.OpenAPITools/Controllers/DefaultApi.cs

expected: an array or collection of IFormFile as an argument in the generated function
actual function signature is ExamplePost(IFormFile filename)