crane: Pulling by digest leads to a changed image when storing on disk

[jastBytes]

Describe the bug

When using crane save to store an image which has been pulled by digest, the tool adds a tag "i-was-a-digest" to the image. This changes the image and so changes the digest of the image on disk. That is unexpected and should not happen.

$ ./crane version
0.19.1
$ ./crane pull icr.io/instana/k8sensor@sha256:85a9ed3a6f2e36facc5a7e7e112c1a91449c8eca3fa7824d4fb32491d50f59ef k8sensor.tar
$ ./crane digest --tarball k8sensor.tar 
sha256:06a3b6e8a8d4bbed52a50206fee94071eb8db06081c0835c1694d0ce399ec72c

As you can see sha256:06a3b6e8a8d4bbed52a50206fee94071eb8db06081c0835c1694d0ce399ec72c is not the digest of the originally image pulled.