malcontent's OCI image scanning could expose registry credentials

malcontent discovers supply-chain compromises through. context, differential analysis, and YARA. Starting in version 0.10.0 and prior to version 1.20.3, malcontent could be made to expose Docker registry credentials if it scanned a specially crafted OCI image reference. malcontent uses google/go-containerregistry for OCI image pulls, which by default uses the Docker credential keychain. A malicious registry could return a `WWW-Authenticate` header redirecting token authentication to an attacker-controlled endpoint, causing credentials to be sent to that endpoint. Version 1.20.3 fixes the issue by defaulting to anonymous auth for OCI pulls.