[BUG] [Spring] Mono<Flux<Item> is generated instead of Flux<Item> when reactive is enabled

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

With the Spring generator, with reactive enabled and responseEntity disabled.
The generated server code for operations returning array of elements must be Flux<Item> and not Mono<Flux<Item>>

openapi-generator version

7.0.1

OpenAPI declaration file content or url

modules/openapi-generator/src/test/resources/3_0/spring/petstore-with-fake-endpoints-models-for-testing.yaml

Generation Details

Sample config file: modules/openapi-generator/src/test/resources/3_0/spring/petstore-with-fake-endpoints-models-for-testing.yaml

Steps to reproduce

Generate and check the return type of the method findPetsByStatus

Related issues/PRs

• #1309

Suggest a fix

Currently, the code assumes that Mono is the response wrapper to always use when reactive is enabled.
This is false when data are arrays.

Start with modules/openapi-generator/src/test/resources/3_0/spring/petstore-with-fake-endpoints-models-for-testing.yaml and generate the Spring server with reactive enabled and responseEntity disabled. Inspect the generated findPetsByStatus method and trace the Spring generator's response-wrapper handling; done means array responses use Flux rather than Mono<Flux>.