Enums in error responses lead to invalid code

When returning enums from an error like this

```json
{
"openapi": "3.0.1",
"info": {
"title": "N/A",
"version": "0.0.0"
},
"paths": {
"/health/live": {
"get": {
"tags": [
"Health"
],
"operationId": "GetLiveHealthStatus",
"responses": {
"200": {
"description": "Success",
"content": {
"text/plain": {
"schema": {
"$ref": "#/components/schemas/HealthStatus"
}
}
}
},
"503": {
"description": "Server Error",
"content": {
"text/plain": {
"schema": {
"$ref": "#/components/schemas/HealthStatus"
}
}
}
}
}
}
}
},
"components": {
"schemas": {
"HealthStatus": {
"enum": [
"Unhealthy",
"Degraded",
"Healthy"
],
"type": "string"
}
}
}
}
```

it generates invalid C# (at least, haven't tried with the other languages)

```csharp
#if NETSTANDARD2_1_OR_GREATER || NETCOREAPP3_1_OR_GREATER
#nullable enable
public async Task GetAsync(Action? requestConfiguration = default, CancellationToken cancellationToken = default) {
#nullable restore
#else
public async Task GetAsync(Action requestConfiguration = default, CancellationToken cancellationToken = default) {
#endif
var requestInfo = ToGetRequestInformation(requestConfiguration);
var errorMapping = new Dictionary> {
{"503", HealthStatus?.CreateFromDiscriminatorValue},
};
return await RequestAdapter.SendPrimitiveAsync(requestInfo, errorMapping, cancellationToken);
}
```

the error given is `'HealthStatus' is a type, which is not valid in the given context`. There is no CreateFromDiscriminatorValue to call.

Reproduce the issue with the supplied OpenAPI document and inspect the generator path that builds error mappings for enum responses in the C# output. Done means the generated client compiles and correctly represents the 503 enum error response without referencing a nonexistent CreateFromDiscriminatorValue member.

Written by the indexing model from the issue text.