Previously attempting to use S3 server side encryption headers
(e.g. `x-amz-server-side-encryption`) would fail when attempting to use
`File#copy` because the method would pass these headers to the UploadPartCopy
(https://docs.aws.amazon.com/AmazonS3/latest/API/API_UploadPartCopy.html)
API call. However, this would fail with an error:
```
<Code>InvalidArgument</Code>
<Message>x-amz-server-side-encryption header is not supported for this operation.</Message>
<ArgumentName>x-amz-server-side-encryption</ArgumentName>
<ArgumentValue>AES256</ArgumentValue>
```
This header can and should be used in the CompleteMultipartUpload
call. To support this, we filter out unknown headers in the
UploadPartCopy.
3546408e47