Harmonize security considerations

[danvangeest]

Harmonize Security Considerations section between this and draft-ietf-lamps-kyber-certificates.

[seanturner]

Agreed. I went for the refer to draft-sfluhrer-cfrg-ml-kem-security-considerations, but that might be overkill. At a minimum, it adds a dependency. Also, not sure how the IESG will react to an informative reference for all of the security considerations.