Add tests for _gej_cmov
Add tests for _gej_cmov

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