Trailing underscore gets removed while parsing

[zellidev0]

Description of the bug

Parsing the following spec produces invalid dart code. The error is, that the class attribute package_ gets renamed to package but this one already exists.

Steps to reproduce

parse this file.

{
    "openapi": "3.0.1",
    "info": {
        "title": "my-service",
        "version": "1.0"
    },
    "servers": [
        {
            "url": "/my-service"
        }
    ],
    "security": [
        {
            "Authorization": []
        }
    ],
    "paths": {
        "/api/v2/subscription/cancel": {
            "delete": {
                "tags": [
                    "subscription-v-2-controller"
                ],
                "operationId": "cancelSubscription_2",
                "responses": {
                    "200": {
                        "description": "OK"
                    }
                }
            }
        }
    },
    "components": {
        "schemas": {
            "WechatPayRedirectToAndroidApp": {
                "type": "object",
                "properties": {
                    "timestamp": {
                        "type": "string"
                    },
                    "package_": {
                        "type": "string"
                    },
                    "package": {
                        "type": "string"
                    }
                }
            }
        }
    }
}

@Openapi(
  additionalProperties: AdditionalProperties(
    pubName: 'openapi_my_service',
  ),
  alwaysRun: true,
  inputSpecFile: 'lib/src/common/openapi_specs/my_service.json',
  generatorName: Generator.dart,
  outputDirectory: '../generated/my_service/',
)
class MyServiceOpenapiGeneratorConfig {}

Expected behavior

The variable gets not renamed, or I have the option to specify how it will be renamed.

Logs

:::::::::::::::::::::::::::::::::::::::::::
::      Openapi generator for dart       ::
:::::::::::::::::::::::::::::::::::::::::::

[INFO] openapi_generator on lib/src/common/openapi_clients.dart:Running following command to generate openapi client - [ generate -o=../generated/my_service/ -i=lib/src/common/openapi_specs/my_service.json -g=dart --additional-properties=allowUnicodeIdentifiers=false,ensureUniqueParams=true,useEnumExtension=true,prependFormOrBodyParameters=false,pubName=openapi_my_service,legacyDiscriminatorBehavior=true,sortModelPropertiesByRequiredFlag=true,sortParamsByRequiredFlag=true,wrapper=none ]
[INFO] openapi_generator on lib/src/common/openapi_clients.dart:Openapi generator completed successfully.
[INFO] openapi_generator on lib/src/common/openapi_clients.dart:Installing dependencies with generated source. flutter pub get
[INFO] openapi_generator on lib/src/common/openapi_clients.dart:Install completed successfully.
[INFO] openapi_generator on lib/src/common/openapi_clients.dart:Skipping source gen because generator does not need it.
[INFO] openapi_generator on lib/src/common/openapi_clients.dart:

### Screenshots

_No response_

### Platform

macOS

### Library version

4.12.1

### Flutter version

3.13.4

### Flutter channel

stable

### Additional context

_No response_