ToPrivateSend does not work with keyring

[ferrell-code]

Below snippet will fail. Keyring does not work when passed as Signer. This was tested in node environment

 // Create a keyring instance
 const keyring = new Keyring({ type: "sr25519" });
 const alice = keyring.addFromUri("//Alice");

 const dolphinId = new BN(1);
 const thousandDol = new BN("1000000000000000000000");
 const toPrivateTx = await privateWallet.toPrivateSend(
    dolphinId,
    thousandDol,
    alice,
    alice.address
  );

However this script does work:

 // Create a keyring instance
 const keyring = new Keyring({ type: "sr25519" });
 const alice = keyring.addFromUri("//Alice");

 const dolphinId = new BN(1);
 const thousandDol = new BN("1000000000000000000000");
 const toPrivateTx = await privateWallet.toPrivateBuild(
    dolphinId,
    thousandDol,
    alice,
    alice.address
  );
 
 await toPrivateTx?.txs[0].signAndSend(alice, {});