[BUG] C# generator creates invalid property signature for nullable dictionaries

We're having the issue the the ASP.NET c# code generator returns a wrong format for nullable dictionaries. Right now, the output is as follows:

public Dictionary?<string, string> MyProperty { get; set; }

However, in c#, the ? has to be placed behind th data type. So the correct format would be:

public Dictionary<string, string>? MyProperty { get; set; }

Here's the example model in TypeSpec and OpenAPI:

model TestModel {
  myProperty?: Record<string> | null;
}

openapi: 3.0.0
info:
  title: (title)
  version: 0.0.0
tags: []
paths: {}
components:
  schemas:
    TestModel:
      type: object
      properties:
        myProperty:
          type: object
          additionalProperties:
            type: string
          nullable: true

Use the provided TypeSpec model and OpenAPI document as the reproduction input for the C# generator. Compare the generated property declaration with the expected nullable dictionary signature; done means the output places the nullable marker after the dictionary type and remains valid C#.