etag is not a required object property in the S3 API, but S3Client assumes it will always be present

[srstsavage]

Some S3 providers may not provide the non-required etag on Objects, but currently S3Client's _get_metadata assumes that ETag will always be present on the HEAD response.

https://docs.aws.amazon.com/AmazonS3/latest/API/API_Object.html

cloudpathlib/cloudpathlib/s3/s3client.py

Line 157 in 9d5fa70

"etag": data["ETag"],

If an S3 client doesn't return ETag on the HeadObject, this results in KeyError: 'ETag' when trying to open an S3Path.

[pjbull]

We'd take a fix with .get("ETag", None)