Add seckey extraction from keypair to the extrakeys tests
Add seckey extraction from keypair to the extrakeys tests

ElementsProject/secp256k1-zkp,afk11/secp256k1,evoskuil/secp256k1,afk11/secp256k1,evoskuil/secp256k1,bitcoin-core/secp256k1,bitcoin/secp256k1,afk11/secp256k1,evoskuil/secp256k1,afk11/secp256k1,bitcoin/secp256k1,bitcoin-core/secp256k1,peterdettman/secp256k1,bitcoin/secp256k1,evoskuil/secp256k1,bitcoin/secp256k1,peterdettman/secp256k1,ElementsProject/secp256k1-zkp,afk11/secp256k1,evoskuil/secp256k1,bitcoin/secp256k1