vsock: cargo-audit reports that `yaml-rust` is unmaintained

[stefano-garzarella]

In vhost-device-vsock we use the config crate which now has a dependency that is unmaintained as cargo audit is reporting.

I reported to them here: https://github.com/mehcode/config-rs/issues/553

For now we don't have a new version available, so we can wait a bit or find an alternative.