More information about this security flaw is available in the following bug: https://bugzilla.redhat.com/show_bug.cgi?id=2369303 Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.
It looks like this is a false positive - the "idna" crate is mentioned in Cargo.lock files, but is not actually pulled in for the build, and it is not vendored either.