2.5.1 testing: gpg export secret key error on cv25519/v5

[Dongsheng Song]

Hi,

I'm running tests for GnuPG 2.5.1 on and I found that the gpg export
secret key error on cv25519/v5 has a regression:

gpgconf --kill all;

export PP='abc'
export GNUPGHOME=$(mktemp -d)

cd ${GNUPGHOME}; gpg -K; ls -ogA

fpr=$(gpg --quick-gen-key --batch --passphrase="${PP}" "X25519 User
<x25519 at example.com>" Ed25519/v5 cert,sign 1y 2>&1 | grep -oE
'[0-9A-Z]{40,}'); \
gpg --export-secret-keys --batch --passphrase="${PP}" --pinentry-mode
loopback ${fpr} > ${fpr}-k1.gpg; ls -ogA

gpg --quick-add-key --batch --passphrase="${PP}" --pinentry-mode
loopback ${fpr} cv25519/v5 encrypt 1y; \
gpg --export-secret-keys --batch --passphrase="${PP}" --pinentry-mode
loopback ${fpr} > ${fpr}-k2.gpg; ls -ogA

The subkey 'cv25519/v5' create succeed, but export secret key error:
gpg: key 0058C8910A40CF407D347314C6399236C1B0CFAC: error receiving key
from agent: Bad public key - skipped

I had checked with GnuPG 2.4.5, no such errors, then this is a regression.

Thanks,
Dongsheng