[BUG] Elm Discriminator generates non-existent exports

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?

Description

When generating Elm code for something that uses a discriminator it add some non-existent things to the exposing (...) list in the Data.elm file.

openapi-generator version

6.6.0

❯ openapi-generator-cli --version
openapi-generator-cli 6.6.0
  commit : 7f8b853
  built  : -999999999-01-01T00:00:00+18:00
  source : https://github.com/openapitools/openapi-generator
  docs   : https://openapi-generator.tech/

OpenAPI declaration file content or url

https://gist.github.com/TheOddler/6cc108f76c5c123900f9741af0bb408b

Generation Details

❯ openapi-generator-cli generate -g elm -i backend/openapi/openapi-bug-mininal.json -o frontend/generated

Steps to reproduce

1. Download the above linked content, and generate elm code from it.
2. Open the src/Api/Data.elm file
3. See that it added ExampleTag(..) and exampleTagVariants to the exposed stuff
4. Notice that neither of those actually exist in the file anywhere else

Related issues/PRs

Suggest a fix

I think those two exports should just not be added, then everything works (at least manually doing that seems to have fixed it for me).

Reproduce the issue with the linked OpenAPI declaration using openapi-generator-cli generate -g elm, then inspect the generated src/Api/Data.elm file. The fix is complete when ExampleTag(..) and exampleTagVariants are no longer listed in exposing (...) unless they are actually defined.