Deleting container not working

When trying to delete a container using DELETE on /v2/abergmeier/alpine/manifests/sha256:e7d88de73db3d3fd9b2d63aa7f447a10fd0220b7cbf39803c803f2af9ba256b3 I get:

{“errors”:[{“code”:“UNSUPPORTED”,“message”:“The operation is unsupported.”}]}
(405 Method Not Allowed)

I would assume that GitHub implements OCI spec properly thus I am wondering whether I am doing something wrong.