Slashes in tag gives a repository error instead of a tag error

We were using $CI_COMMIT_REF_NAME in a CI pipeline as our tag and someone used '/' in their branch name.

The error we got was:
`repository can only contain the runes `abcdefghijklmnopqrstuvwxyz0123456789_-./`: /registry.exampleurl.com/private/repo-name:test/withslash`

We've corrected our pipeline, but it would be nice to see the error happen on the forbidden character in the tag rather than failing on the repository check.