[BUG][aspnetcore] multi-file upload only presents one file

Created by: hauntingEcho

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?
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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

Save the above file as example.yml
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
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)