GitHubActions cache for Docker images may be broken

[bajtos]

Quoting from https://github.com/CheckerNetwork/node/actions/runs/14617308991/job/41008380518?pr=727#step:7:178

#4 importing cache manifest from ghcr.io/CheckerNetwork/node
#4 ERROR: failed to configure registry cache importer: invalid reference format: repository name (CheckerNetwork/node) must be lowercase

[bajtos]

Potentially helpful content:

• https://stackoverflow.com/a/74924069
• Repository/image name should be lowercased automatically in cache parameters. docker/build-push-action#424