Field with Optional[Enum] does not have correct Avro representation after using .avro_schema()

[bartpijn]

Describe the bug
When describing a (pydantic) dataclass with a field that either is None or some Enum-value, the generated avro schema for this field does not have the correct types.

To Reproduce
Consider the following data model:

from enum import Enum
from typing import Optional

from dataclasses_avroschema.avrodantic import AvroBaseModel


class Locale(str, Enum):
    en_us = 'en_us'
    de_de = 'de_de'


class Translation(AvroBaseModel):
    locale: Locale
    value: str
    localization_source: Optional[str]
    original_locale: Optional[Locale]


print(Translation.avro_schema())

The print:

{
  "type": "record",
  "name": "Translation",
  "fields": [
    {
      "name": "locale",
      "type": {
        "type": "enum",
        "name": "locale",
        "symbols": [
          "en_us",
          "de_de"
        ]
      }
    },
    {
      "name": "value",
      "type": "string"
    },
    {
      "name": "localization_source",
      "type": [
        "null",
        "string"
      ],
      "default": null
    },
    {
      "name": "original_locale",
      "type": {
        "type": "enum",
        "name": "original_locale",
        "symbols": [
          "en_us",
          "de_de"
        ]
      },
      "default": null
    }
  ]
}

Expected behavior
Expected output:

{
  "type": "record",
  "name": "Translation",
  "fields": [
    {
      "name": "locale",
      "type": {
        "type": "enum",
        "name": "locale",
        "symbols": [
          "en_us",
          "de_de"
        ]
      }
    },
    {
      "name": "value",
      "type": "string"
    },
    {
      "name": "localization_source",
      "type": [
        "null",
        "string"
      ],
      "default": null
    },
    {
      "name": "original_locale",
      "type": {
        "type": [
          "null", \\ THIS IS THE CHANGE
          "enum"
        ],
        "name": "original_locale",
        "symbols": [
          "en_us",
          "de_de"
        ]
      },
      "default": null
    }
  ]
}

My environment
Python 3.9.15
Pydantic 1.10.2
dataclasses-avroschema 0.34.3
avro 1.11.1