SourceMany unexpected behavior

[Fylhtq42]

NEST/Elasticsearch.Net version: 7.3.0

Elasticsearch version: 7.2

Description of the problem including expected versus actual behavior:
I used Nest.IElasticClient for search by SourceMany and found some
strange behavior. Api of method looks like you can send ids and you will get IEnumerable back. But if you send ["id1","id1","id1"] and Index contains one document with id = "id1", you will get 9 documents back instead of 3 for example. Because if you send multi get request to elastic api with 3 same ids you will get 3 documents in response. And I found that you have some join operation after elastic api response in MultiGetResponse.SourceMany, it creates duplicates.

Steps to reproduce:

1. Save one document to index with Id = "id1"
2. Call elasticClient.SourceMany(ids, IndexName);
   Ids = ["id1","id1","id1"]
3. You get 9 documents back.

[russcam]

This does look like a bug, which we will look to fix.

[Fylhtq42]

Thank you for answering my issue, @russcam.