Fix deserialization with missing XML namespace

[BaerMitUmlaut]

Some S3 implementations do not include the XML namespace in their responses:

<?xml version="1.0" encoding="UTF-8"?>
<CopyObjectResult>
    <LastModified>
        2022-10-29T15:34:41.626Z
    </LastModified>
    <ETag>
        &#34;ead3fcd881dee32547f1b6ca1fc29463&#34;
    </ETag>
</CopyObjectResult>

minio-dotnet fails to deserialize such a response, this PR fixes that.

I encountered this issue in the wild, I'm guessing my provider uses seaweedfs, which has fixed this just hours ago: seaweedfs/seaweedfs#6676
However, they might not be the only ones with that behaviour.