[scala-sttp]Update import for enum in API class

Created by: bgong-mdsol

This PR fixes the issue #14545

Here is the openapi spec that can be used to reproduce the issue and verify the fix.

openapi: 3.0.3
info:
  title: parameter type is enum
  version: '1.0'
paths:
  /state:
    get:
      operationId: getBooks
      parameters:
      - explode: true
        in: query
        name: language
        required: false
        schema:
          $ref: '#/components/schemas/LanguageCode'
      responses:
        '200':
          description: get Books
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Books'
components:
  schemas:
    Books:
      properties:
        title:
          type: string
        language:
          $ref: '#/components/schemas/LanguageCode'
        author:
          type: string
      type: object
    LanguageCode:
      enum:
      - eng
      - jpn
      title: language_code
      type: string

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package 
  ./bin/generate-samples.sh
  ./bin/utils/export_docs_generators.sh

  Commit all changed files. This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master. These must match the expectations made by your contribution. You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*. For Windows users, please run the script in Git BASH.
• File the PR against the correct branch: master (6.3.0) (minor release - breaking changes with fallbacks)
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.
• - [ ] @chameleon82 @clasnake @jimschubert @shijinkui @ramzimaalej @Bouillie @wing328 @jcarres-mdsol