ElasticLowLevelClient returns the same VoidResponse instance from subsequent requests

[t3j3x6]

Elasticsearch.Net: 6.0.0 through 6.5.0. Does not reproduce on 5.6.5.
Elasticsearch version: 6.6.0

When using the VoidResponse response type, each request returns the same VoidResponse instance, modifying its ApiCall property. For StringResponse, BytesResponse and DynamicResponse a new instance is returned. Using a different ElasticLowLevelClient instance does not change this behavior. Here's a small demonstration:

var connectionConfiguration = new ConnectionConfiguration(
	new SingleNodeConnectionPool(new Uri("http://127.0.0.1:9200")),
	new HttpConnection());
var client = new ElasticLowLevelClient(connectionConfiguration);

var voidResponse1 = await client.IndicesCreateAsync<VoidResponse>("foo", null);
var originalApiCall = voidResponse1.ApiCall;
Console.WriteLine($"{voidResponse1.HttpMethod}"); // PUT

var voidResponse2 = await client.IndicesDeleteAsync<VoidResponse>("foo");
var modifiedApiCall = voidResponse1.ApiCall;
Console.WriteLine($"{voidResponse1.HttpMethod}"); // DELETE

Console.WriteLine($"{ReferenceEquals(voidResponse1, voidResponse2)}"); // true
Console.WriteLine($"{ReferenceEquals(originalApiCall, modifiedApiCall)}"); // false

var stringResponse1 = await client.IndicesCreateAsync<StringResponse>("foo", null);
var stringResponse2 = await client.IndicesDeleteAsync<StringResponse>("foo");
Console.WriteLine($"{ReferenceEquals(stringResponse1, stringResponse2)}"); // false

var byteResponse1 = await client.IndicesCreateAsync<BytesResponse>("foo", null);
var byteResponse2 = await client.IndicesDeleteAsync<BytesResponse>("foo");
Console.WriteLine($"{ReferenceEquals(byteResponse1, byteResponse2)}"); // false

var dynamicResponse1 = await client.IndicesCreateAsync<DynamicResponse>("foo", null);
var dynamicResponse2 = await client.IndicesDeleteAsync<DynamicResponse>("foo");
Console.WriteLine($"{ReferenceEquals(dynamicResponse1, dynamicResponse2)}"); // false

[Mpdreamz]

Thank you for reporting this @t3j3x6 opened #3588 to address this.