oras client and Go SDK fail when registry responds with chunked transfer encoding

[AaronFriel]

To reproduce, use the Zot registry and push a manifest of >= 2000 bytes, as shown below:

# start Zot in one shell
docker run -p 5000:5000 ghcr.io/project-zot/zot-linux-amd64:latest

# in another shell

# start in an empty temp dir
cd $(mktemp -d)

# create 20 test artifacts:
for f in $(seq 1 20); do echo "$f" > "artifact-${f}.txt"; done

# push those to a zot registry:
oras push localhost:5000/foo/bar:v1.0 artifact-*.txt

# fetch the manifest
oras manifest fetch localhost:5000/foo/bar:v1.0
# Error: GET "http://localhost:5000/v2/foo/bar/manifests/v5.21.1": unknown response Content-Length