title: RestSharp AddHeader not working
body: <p>I am building a simple REST/Json windows client using C# and RestSharp 105.2.3.  Everything is working beautifully but the additional HTTP header I am specifying does not seem to being added according to the Wireshark trace.  Am I missing something or is there an underlying HTTP method I should use?</p>
  
  <p>The code is straightforward as outlined below and I cannot see the RequestId header in the trace:</p>
  
  <pre><code>    var client = new RestClient("http://example.com");
      client.Authenticator = new HttpBasicAuthenticator("username", password");
  
      var requestParams = new RequestItem
      { Parameter1 = "test1", Parameter2 = "test2" };
  
      var request = new RestRequest("/sample/", Method.POST);
      request.AddHeader("RequestId", "value");
  
      request.RequestFormat = DataFormat.Json;
      request.Parameters.Clear();
      var requestParamsJson = request.JsonSerializer.Serialize(requestParams);
      request.AddParameter("application/json; charset=utf-8", requestParamsJson, ParameterType.RequestBody);
      IRestResponse&lt;ResponseItem&gt; response = client.Execute&lt;ResponseItem&gt;(request);
  </code></pre>