Wrong mapping of the ed25519 keys to cv25519 policy value

As found out during the RPM testing in

https://github.com/rpm-software-management/rpm/pull/4020#discussion_r2489425787

there seems to be copy&paste error in mapping the key ed25519 key type to policy value of the cv25519 for the ECC keys (v4):

https://gitlab.com/sequoia-pgp/sequoia/-/blob/main/openpgp/src/policy.rs?ref_type=heads#L1574

The v6 mapping (where the Ed25519 is a separate algorithm ID) looks ok.

This is most likely a copy&paste error.