[BUG] Library spring-boot generates incorrect Java syntax

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

openapi-generator version

id 'org.openapi.generator' version "5.2.1"

OpenAPI declaration file content or url

swagger: '2.0'
info:
  version: '1.0.0'
  title: Example API
  contact:
    name: No Name
    email: example@example.com
    url: https://example.com
host: example.com
schemes:
  - https

basePath: /v2

paths:
  /photos:
    post:
      summary: Photo upload
      consumes:
        - multipart/form-data
      description: |
      parameters:
        - name: "photo[content]"
          in: formData
          description: file
          required: true
          type: file
      responses:
        201:
          description: Success
          schema:
            type: object
            properties:
              photo:
                type: object
                properties:
                  id:
                    type: string
                    description: Photo ID

Generation Details

Config options:

[
        dateLibrary: "java8-localdatetime",
        skipDefaultInterface: "true",
        serializableModel: "true",
        interfaceOnly: "true",
        hideGenerationTimestamp: "true",
        useTags: "true",
        library: "spring-boot",
        reactive: "true"
]

Steps to reproduce

The generation result is:

@javax.annotation.Generated(value = "org.openapitools.codegen.languages.SpringCodegen")
@Validated
@Api(value = "Default", description = "the Default API")
public interface DefaultApi {

    /**
     * POST /photos : Photo upload
     *
     * @param photoContent file (required)
     * @return Success (status code 201)
     */
    @ApiOperation(value = "Photo upload", nickname = "photosPost", notes = "", response = InlineResponse201.class, tags={  })
    @ApiResponses(value = { 
        @ApiResponse(code = 201, message = "Success", response = InlineResponse201.class) })
    @RequestMapping(
        method = RequestMethod.POST,
        value = "/photos",
        produces = { "*/*" },
        consumes = { "multipart/form-data" }
    )
    Mono<ResponseEntity<InlineResponse201>> photosPost(@ApiParam(value = "file") @Valid @RequestPart(value = "photo[content]", required = true) Flux<Part> photo[content], @ApiIgnore final ServerWebExchange exchange);

}

Look at Flux<Part> photo[content] - it is not correct java syntax. Flux<Part> photoContent is expected.

Changing library option from spring-boot to spring-cloud solves problem, but reactive:"true" is necessary for me and it can be used only with spring-boot

Start by reproducing generation with the supplied OpenAPI YAML, the spring-boot library, and reactive=true using openapi-generator 5.2.1. Trace how the form-data parameter name photo[content] becomes the generated Java parameter, then verify that the output uses a valid identifier such as photoContent and remains compilable.