[BUG][csharp-netcore] CodegenProperty isString is incorrectly true

Doubles sometimes have isString == true. Please see enum EnumTest.EnumNumberEnum

{{! below has #isNumeric as a work around but should probably have ^isString instead https://github.com/OpenAPITools/openapi-generator/issues/15038}}
return {{#isInnerEnum}}{{classname}}.{{/isInnerEnum}}{{{datatypeWithEnum}}}ToJsonValue({{#lambda.camelcase_param}}{{classname}}{{{datatypeWithEnum}}}{{/lambda.camelcase_param}}){{#isNumeric}}.ToString(){{/isNumeric}};

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Description

openapi-generator version

OpenAPI declaration file content or url

Generation Details

Steps to reproduce

Related issues/PRs

Suggest a fix

Start with the C# code-generation path for enum EnumTest.EnumNumberEnum and inspect how CodegenProperty assigns isString and isNumeric. Compare the generated ToJsonValue expression shown in the issue with the expected handling for doubles. Done means a reproducible case no longer marks the double as a string and the generated serialization uses the correct condition.