ignore tags when digest present

[jmorgancusick]

Expected behavior

If I run

container-diff analyze postgres:11-alpine@sha256:f85c0e55cc917bb76083a92a4cc5f1af080298eb5a1f5449a8dc8665f7fef48e

I expect analyze info to be printed

Actual behavior

container-diff errors out with the following log:

ERRO[0000] error retrieving image postgres:11-alpine@sha256:f85c0e55cc917bb76083a92a4cc5f1af080298eb5a1f5449a8dc8665f7fef48e: parsing image reference: could not parse reference

Information

• container-diff version: v0.15.0

• Operating system:

Distributor ID:	Ubuntu
Description:	Ubuntu 18.04.4 LTS
Release:	18.04
Codename:	bionic

Steps to reproduce the behavior

1. Run container-diff analyze postgres@sha256:f85c0e55cc917bb76083a92a4cc5f1af080298eb5a1f5449a8dc8665f7fef48e and notice that it runs fine
2. Run with the optional digest container-diff analyze postgres:11-alpine@sha256:f85c0e55cc917bb76083a92a4cc5f1af080298eb5a1f5449a8dc8665f7fef48e and notice the error message

[nkubala]

hmm, at first glance this looks like it could be a go-containerregistry bug? that's what we use for all our image handling, and I don't think we do any preprocessing of tags before we pass the reference over to it

[NVolcz]

I experienced the same issue today with ghcr.io.